Multiply perfect number

Last updated October 24, 2024

In mathematics, a multiply perfect number (also called multiperfect number or pluperfect number) is a generalization of a perfect number.

For a given natural number k, a number n is called k-perfect (or k-fold perfect) if the sum of all positive divisors of n (the divisor function, σ(n)) is equal to kn; a number is thus perfect if and only if it is 2-perfect. A number that is k-perfect for a certain k is called a multiply perfect number. As of 2014, k-perfect numbers are known for each value of k up to 11.^[1]

It is unknown whether there are any odd multiply perfect numbers other than 1. The first few multiply perfect numbers are:

1, 6, 28, 120, 496, 672, 8128, 30240, 32760, 523776, 2178540, 23569920, 33550336, 45532800, 142990848, 459818240, ... (sequence A007691 in the OEIS ).

Example

The sum of the divisors of 120 is

1 + 2 + 3 + 4 + 5 + 6 + 8 + 10 + 12 + 15 + 20 + 24 + 30 + 40 + 60 + 120 = 360

which is 3 × 120. Therefore 120 is a 3-perfect number.

Smallest known k-perfect numbers

The following table gives an overview of the smallest known k-perfect numbers for k ≤ 11 (sequence A007539 in the OEIS ):

k	Smallest k-perfect number	Factors	Found by
1	1		ancient
2	6	2 × 3	ancient
3	120	2³ × 3 × 5	ancient
4	30240	2⁵ × 3³ × 5 × 7	René Descartes, circa 1638
5	14182439040	2⁷ × 3⁴ × 5 × 7 × 11² × 17 × 19	René Descartes, circa 1638
6	154345556085770649600 (21 digits)	2¹⁵ × 3⁵ × 5² × 7² × 11 × 13 × 17 × 19 × 31 × 43 × 257	Robert Daniel Carmichael, 1907
7	141310897947438348259849...523264343544818565120000 (57 digits)	2³² × 3¹¹ × 5⁴ × 7⁵ × 11² × 13² × 17 × 19³ × 23 × 31 × 37 × 43 × 61 × 71 × 73 × 89 × 181 × 2141 × 599479	TE Mason, 1911
8	826809968707776137289924...057256213348352000000000 (133 digits)	2⁶² × 3¹⁵ × 5⁹ × 7⁷ × 11³ × 13³ × 17² × 19 × 23 × 29 × 31² × 37 × 41 × 43 × 53 × 61² × 71² × 73 × 83 × 89 × 97² × 127 × 193 × 283 × 307 × 317 × 331 × 337 × 487 × 521² × 601 × 1201 × 1279 × 2557 × 3169 × 5113 × 92737 × 649657	Stephen F. Gretton, 1990^[1]
9	561308081837371589999987...415685343739904000000000 (287 digits)	2¹⁰⁴ × 3⁴³ × 5⁹ × 7¹² × 11⁶ × 13⁴ × 17 × 19⁴ × 23² × 29 × 31⁴ × 37³ × 41² × 43² × 47² × 53 × 59 × 61 × 67 × 71³ × 73 × 79² × 83 × 89 × 97 × 103² × 107 × 127 × 131² × 137² × 151² × 191 × 211 × 241 × 331 × 337 × 431 × 521 × 547 × 631 × 661 × 683 × 709 × 911 × 1093 × 1301 × 1723 × 2521 × 3067 × 3571 × 3851 × 5501 × 6829 × 6911 × 8647 × 17293 × 17351 × 29191 × 30941 × 45319 × 106681 × 110563 × 122921 × 152041 × 570461 × 16148168401	Fred Helenius, 1995^[1]
10	448565429898310924320164...000000000000000000000000 (639 digits)	2¹⁷⁵ × 3⁶⁹ × 5²⁹ × 7¹⁸ × 11¹⁹ × 13⁸ × 17⁹ × 19⁷ × 23⁹ × 29³ × 31⁸ × 37² × 41⁴ × 43⁴ × 47⁴ × 53³ × 59 × 61⁵ × 67⁴ × 71⁴ × 73² × 79 × 83 × 89 × 97 × 101³ × 103² × 107² × 109 × 113 × 127² × 131² × 139 × 149 × 151 × 163 × 179 × 181² × 191 × 197 × 199 × 211³ × 223 × 239 × 257 × 271 × 281 × 307 × 331 × 337 × 353² × 367 × 373 × 397 × 419 × 421 × 521 × 523 × 547² × 613 × 683 × 761 × 827 × 971 × 991 × 1093 × 1741 × 1801 × 2113 × 2221 × 2237 × 2437 × 2551 × 2851 × 3221 × 3571 × 3637 × 3833 × 4339 × 5101 × 5419 × 6577 × 6709 × 7621 × 7699 × 8269 × 8647 × 11093 × 13421 × 13441 × 14621 × 17293 × 26417 × 26881 × 31723 × 44371 × 81343 × 88741 × 114577 × 160967 × 189799 × 229153 × 292561 × 579281 × 581173 × 583367 × 1609669 × 3500201 × 119782433 × 212601841 × 2664097031 × 2931542417 × 43872038849 × 374857981681 × 4534166740403	George Woltman, 2013^[1]
11	251850413483992918774837...000000000000000000000000 (1907 digits)	2⁴⁶⁸ × 3¹⁴⁰ × 5⁶⁶ × 7⁴⁹ × 11⁴⁰ × 13³¹ × 17¹¹ × 19¹² × 23⁹ × 29⁷ × 31¹¹ × 37⁸ × 41⁵ × 43³ × 47³ × 53⁴ × 59³ × 61² × 67⁴ × 71⁴ × 73³ × 79 × 83² × 89 × 97⁴ × 101⁴ × 103³ × 109³ × 113² × 127³ × 131³ × 137² × 139² × 149² × 151 × 157² × 163 × 167 × 173 × 181 × 191 × 193² × 197 × 199 × 211³ × 223 × 227 × 229² × 239 × 251 × 257 × 263 × 269³ × 271 × 281² × 293 × 307³ × 313 × 317 × 331 × 347 × 349 × 367 × 373 × 397 × 401 × 419 × 421 × 431 × 443² × 449 × 457 × 461 × 467 × 491 × 499² × 541 × 547 × 569 × 571 × 599 × 607 × 613 × 647 × 691 × 701 × 719 × 727 × 761 × 827 × 853 × 937 × 967 × 991 × 997 × 1013 × 1061 × 1087 × 1171 × 1213 × 1223 × 1231 × 1279 × 1381 × 1399 × 1433 × 1609 × 1613 × 1619 × 1723 × 1741 × 1783 × 1873 × 1933 × 1979 × 2081 × 2089 × 2221 × 2357 × 2551 × 2657 × 2671 × 2749 × 2791 × 2801 × 2803 × 3331 × 3433 × 4051 × 4177 × 4231 × 5581 × 5653 × 5839 × 6661 × 7237 × 7699 × 8081 × 8101 × 8269 × 8581 × 8941 × 10501 × 11833 × 12583 × 12941 × 13441 × 14281 × 15053 × 17929 × 19181 × 20809 × 21997 × 23063 × 23971 × 26399 × 26881 × 27061 × 28099 × 29251 × 32051 × 32059 × 32323 × 33347 × 33637 × 36373 × 38197 × 41617 × 51853 × 62011 × 67927 × 73547 × 77081 × 83233 × 92251 × 93253 × 124021 × 133387 × 141311 × 175433 × 248041 × 256471 × 262321 × 292561 × 338753 × 353641 × 441281 × 449653 × 509221 × 511801 × 540079 × 639083 × 696607 × 746023 × 922561 × 1095551 × 1401943 × 1412753 × 1428127 × 1984327 × 2556331 × 5112661 × 5714803 × 7450297 × 8334721 × 10715147 × 14091139 × 14092193 × 18739907 × 19270249 × 29866451 × 96656723 × 133338869 × 193707721 × 283763713 × 407865361 × 700116563 × 795217607 × 3035864933 × 3336809191 × 35061928679 × 143881112839 × 161969595577 × 287762225677 × 761838257287 × 840139875599 × 2031161085853 × 2454335007529 × 2765759031089 × 31280679788951 × 75364676329903 × 901563572369231 × 2169378653672701 × 4764764439424783 × 70321958644800017 × 79787519018560501 × 702022478271339803 × 1839633098314450447 × 165301473942399079669 × 604088623657497125653141 × 160014034995323841360748039 × 25922273669242462300441182317 × 15428152323948966909689390436420781 × 420391294797275951862132367930818883361 × 23735410086474640244277823338130677687887 × 628683935022908831926019116410056880219316806841500141982334538232031397827230330241	George Woltman, 2001^[1]

Properties

It can be proven that:

For a given prime number p, if n is p-perfect and p does not divide n, then pn is (p + 1)-perfect. This implies that an integer n is a 3-perfect number divisible by 2 but not by 4, if and only if n/2 is an odd perfect number, of which none are known.
If 3n is 4k-perfect and 3 does not divide n, then n is 3k-perfect.

Odd multiply perfect numbers

It is unknown whether there are any odd multiply perfect numbers other than 1. However if an odd k-perfect number n exists where k > 2, then it must satisfy the following conditions:^[2]

The largest prime factor is ≥ 100129
The second largest prime factor is ≥ 1009
The third largest prime factor is ≥ 101

Bounds

In little-o notation, the number of multiply perfect numbers less than x is $o(x^{\varepsilon })$ for all ε > 0.^[2]

The number of k-perfect numbers n for n ≤ x is less than $cx^{c'\log \log \log x/\log \log x}$ , where c and c' are constants independent of k.^[2]

Under the assumption of the Riemann hypothesis, the following inequality is true for all k-perfect numbers n, where k > 3

\log \log n>k\cdot e^{-\gamma }

where $\gamma$ is Euler's gamma constant. This can be proven using Robin's theorem.

The number of divisors τ(n) of a k-perfect number n satisfies the inequality^[3]

\tau (n)>e^{k-\gamma }.

The number of distinct prime factors ω(n) of n satisfies^[4]

\omega (n)\geq k^{2}-1.

If the distinct prime factors of n are $p_{1},p_{2},\ldots ,p_{r}$ , then:^[4]

r\left({\sqrt[{r}]{3/2}}-1\right)<\sum _{i=1}^{r}{\frac {1}{p_{i}}}<r\left(1-{\sqrt[{r}]{6/k^{2}}}\right),~~{\text{if }}n{\text{ is even}}

r\left({\sqrt[{3r}]{k^{2}}}-1\right)<\sum _{i=1}^{r}{\frac {1}{p_{i}}}<r\left(1-{\sqrt[{r}]{8/(k\pi ^{2})}}\right),~~{\text{if }}n{\text{ is odd}}

Specific values of k

Perfect numbers

A number n with σ(n) = 2n is perfect.

Triperfect numbers

A number n with σ(n) = 3n is triperfect. There are only six known triperfect numbers and these are believed to comprise all such numbers:

120, 672, 523776, 459818240, 1476304896, 51001180160 (sequence A005820 in the OEIS )

If there exists an odd perfect number m (a famous open problem) then 2m would be 3-perfect, since σ(2m) = σ(2) σ(m) = 3×2m. An odd triperfect number must be a square number exceeding 10⁷⁰ and have at least 12 distinct prime factors, the largest exceeding 10⁵.^[5]

Variations

Unitary multiply perfect numbers

A similar extension can be made for unitary perfect numbers. A positive integer n is called a unitary multik-perfectnumber if σ^*(n) = kn where σ^*(n) is the sum of its unitary divisors. (A divisor d of a number n is a unitary divisor if d and n/d share no common factors.).

A unitary multiply perfect number is simply a unitary multi k-perfect number for some positive integer k. Equivalently, unitary multiply perfect numbers are those n for which n divides σ^*(n). A unitary multi 2-perfect number is naturally called a unitary perfect number. In the case k > 2, no example of a unitary multi k-perfect number is yet known. It is known that if such a number exists, it must be even and greater than 10¹⁰² and must have more than forty four odd prime factors. This problem is probably very difficult to settle. The concept of unitary divisor was originally due to R. Vaidyanathaswamy (1931) who called such a divisor as block factor. The present terminology is due to E. Cohen (1960).

The first few unitary multiply perfect numbers are:

1, 6, 60, 90, 87360 (sequence A327158 in the OEIS )

Bi-unitary multiply perfect numbers

A positive integer n is called a bi-unitary multik-perfectnumber if σ^**(n) = kn where σ^**(n) is the sum of its bi-unitary divisors. This concept is due to Peter Hagis (1987). A bi-unitary multiply perfect number is simply a bi-unitary multi k-perfect number for some positive integer k. Equivalently, bi-unitary multiply perfect numbers are those n for which n divides σ^**(n). A bi-unitary multi 2-perfect number is naturally called a bi-unitary perfect number, and a bi-unitary multi 3-perfect number is called a bi-unitary triperfect number.

A divisor d of a positive integer n is called a bi-unitary divisor of n if the greatest common unitary divisor (gcud) of d and n/d equals 1. This concept is due to D. Surynarayana (1972). The sum of the (positive) bi-unitary divisors of n is denoted by σ^**(n).

Peter Hagis (1987) proved that there are no odd bi-unitary multiperfect numbers other than 1. Haukkanen and Sitaramaiah (2020) found all bi-unitary triperfect numbers of the form 2^au where 1 ≤ a ≤ 6 and u is odd,^[6]^[7]^[8] and partially the case where a = 7.^[9]^[10] Further, they fixed completely the case a = 8.^[11]

The first few bi-unitary multiply perfect numbers are:

1, 6, 60, 90, 120, 672, 2160, 10080, 22848, 30240 (sequence A189000 in the OEIS )

Related Research Articles

Amicable numbers are two different natural numbers related in such a way that the sum of the proper divisors of each is equal to the other number. That is, s(a)=b and s(b)=a, where s(n)=σ(n)-n is equal to the sum of positive divisors of n except n itself (see also divisor function).

In number theory, a perfect number is a positive integer that is equal to the sum of its positive proper divisors, that is, divisors excluding the number itself. For instance, 6 has proper divisors 1, 2 and 3, and 1 + 2 + 3 = 6, so 6 is a perfect number. The next perfect number is 28, since 1 + 2 + 4 + 7 + 14 = 28.

In mathematics, a divisor of an integer $also called a factor of is an integer that may be multiplied by some integer to produce In this case, one also says that is a multiple of An integer is divisible or evenly divisible by another integer if is a divisor of; this implies dividing by leaves no remainder.$

<span class="mw-page-title-main">Euler's totient function</span> Number of integers coprime to and less than n

In number theory, Euler's totient function counts the positive integers up to a given integer $n$ that are relatively prime to $n$ . It is written using the Greek letter phi as $or, and may also be called Euler's phi function . In other words, it is the number of integers k in the range 1 \leq k \leq n for which the greatest common divisor gcd(n, k) is equal to 1. The integers k of this form are sometimes referred to as totatives of n .$

A highly composite number is a positive integer that has more divisors than all smaller positive integers. A related concept is that of a largely composite number, a positive integer that has at least as many divisors as all smaller positive integers. The name can be somewhat misleading, as the first two highly composite numbers are not actually composite numbers; however, all further terms are.

In number theory, an abundant number or excessive number is a positive integer for which the sum of its proper divisors is greater than the number. The integer 12 is the first abundant number. Its proper divisors are 1, 2, 3, 4 and 6 for a total of 16. The amount by which the sum exceeds the number is the abundance. The number 12 has an abundance of 4, for example.

In number theory, a deficient number or defective number is a positive integer $n$ for which the sum of divisors of $n$ is less than $2 n$ . Equivalently, it is a number for which the sum of proper divisors is less than $n$ . For example, the proper divisors of 8 are 1, 2, and 4, and their sum is less than 8, so 8 is deficient.

In mathematics, a quasiperfect number is a natural number n for which the sum of all its divisors (the sum-of-divisors function σ(n)) is equal to 2n + 1. Equivalently, n is the sum of its non-trivial divisors (that is, its divisors excluding 1 and n). No quasiperfect numbers have been found so far.

In number theory, a weird number is a natural number that is abundant but not semiperfect. In other words, the sum of the proper divisors of the number is greater than the number, but no subset of those divisors sums to the number itself.

In mathematics, an almost perfect number (sometimes also called slightly defective or least deficientnumber) is a natural number n such that the sum of all divisors of n (the sum-of-divisors function σ(n)) is equal to 2n − 1, the sum of all proper divisors of n, s(n) = σ(n) − n, then being equal to n − 1. The only known almost perfect numbers are powers of 2 with non-negative exponents (sequence A000079 in the OEIS). Therefore the only known odd almost perfect number is 2⁰ = 1, and the only known even almost perfect numbers are those of the form 2^k for some positive integer k; however, it has not been shown that all almost perfect numbers are of this form. It is known that an odd almost perfect number greater than 1 would have at least six prime factors.

In number theory, a $k$ -hyperperfect number is a natural number $n$ for which the equality $holds, where σ (n) is the divisor function (i.e., the sum of all positive divisors of n). A hyperperfect number is a k -hyperperfect number for some integer k . Hyperperfect numbers generalize perfect numbers, which are 1-hyperperfect.$

<span class="mw-page-title-main">Divisor function</span> Arithmetic function related to the divisors of an integer

In mathematics, and specifically in number theory, a divisor function is an arithmetic function related to the divisors of an integer. When referred to as the divisor function, it counts the number of divisors of an integer. It appears in a number of remarkable identities, including relationships on the Riemann zeta function and the Eisenstein series of modular forms. Divisor functions were studied by Ramanujan, who gave a number of important congruences and identities; these are treated separately in the article Ramanujan's sum.

In mathematics, a harmonic divisor number or Ore number is a positive integer whose divisors have a harmonic mean that is an integer. The first few harmonic divisor numbers are

A unitary perfect number is an integer which is the sum of its positive proper unitary divisors, not including the number itself. Some perfect numbers are not unitary perfect numbers, and some unitary perfect numbers are not ordinary perfect numbers.

In mathematics, an untouchable number is a positive integer that cannot be expressed as the sum of all the proper divisors of any positive integer. That is, these numbers are not in the image of the aliquot sum function. Their study goes back at least to Abu Mansur al-Baghdadi, who observed that both 2 and 5 are untouchable.

In number theory, a practical number or panarithmic number is a positive integer $such that all smaller positive integers can be represented as sums of distinct divisors of . For example, 12 is a practical number because all the numbers from 1 to 11 can be expressed as sums of its divisors 1, 2, 3, 4, and 6: as well as these divisors themselves, we have 5 = 3 + 2, 7 = 6 + 1, 8 = 6 + 2, 9 = 6 + 3, 10 = 6 + 3 + 1, and 11 = 6 + 3 + 2.$

In number theory, a colossally abundant number is a natural number that, in a particular, rigorous sense, has many divisors. Particularly, it is defined by a ratio between the sum of an integer's divisors and that integer raised to a power higher than one. For any such exponent, whichever integer has the highest ratio is a colossally abundant number. It is a stronger restriction than that of a superabundant number, but not strictly stronger than that of an abundant number.

In number theory, friendly numbers are two or more natural numbers with a common abundancy index, the ratio between the sum of divisors of a number and the number itself. Two numbers with the same "abundancy" form a friendly pair; n numbers with the same abundancy form a friendly n-tuple.

In mathematics, a natural number a is a unitary divisor of a number b if a is a divisor of b and if a and $are coprime, having no common factor other than 1. Equivalently, a divisor a of b is a unitary divisor if and only if every prime factor of a has the same multiplicity in a as it has in b .$

In number theory, a superperfect number is a positive integer $n$ that satisfies

References

1 2 3 4 5 Flammenkamp, Achim. "The Multiply Perfect Numbers Page" . Retrieved 22 January 2014.
1 2 3 Sándor, Mitrinović & Crstici 2006 , p. 105
↑ Dagal, Keneth Adrian P. (2013). "A Lower Bound for τ(n) for k-Multiperfect Number". arXiv: 1309.3527 [math.NT].
1 2 Sándor, Mitrinović & Crstici 2006 , p. 106
↑ Sándor, Mitrinović & Crstici 2006 , pp. 108–109
↑ Haukkanen & Sitaramaiah 2020a
↑ Haukkanen & Sitaramaiah 2020b
↑ Haukkanen & Sitaramaiah 2020c
↑ Haukkanen & Sitaramaiah 2020d
↑ Haukkanen & Sitaramaiah 2021a
↑ Haukkanen & Sitaramaiah 2021b

Sources

Broughan, Kevin A.; Zhou, Qizhi (2008). "Odd multiperfect numbers of abundancy 4" (PDF). Journal of Number Theory. 126 (6): 1566–1575. doi:10.1016/j.jnt.2007.02.001. hdl: 10289/1796 . MR 2419178.
Guy, Richard K. (2004). Unsolved problems in number theory (3rd ed.). Springer-Verlag. B2. ISBN 978-0-387-20860-2. Zbl 1058.11001.
Haukkanen, Pentti; Sitaramaiah, V. (2020a). "Bi-unitary multiperfect numbers, I" (PDF). Notes on Number Theory and Discrete Mathematics. 26 (1): 93–171. doi: 10.7546/nntdm.2020.26.1.93-171 .
Haukkanen, Pentti; Sitaramaiah, V. (2020b). "Bi-unitary multiperfect numbers, II" (PDF). Notes on Number Theory and Discrete Mathematics. 26 (2): 1–26. doi: 10.7546/nntdm.2020.26.2.1-26 .
Haukkanen, Pentti; Sitaramaiah, V. (2020c). "Bi-unitary multiperfect numbers, III" (PDF). Notes on Number Theory and Discrete Mathematics. 26 (3): 33–67. doi: 10.7546/nntdm.2020.26.3.33-67 .
Haukkanen, Pentti; Sitaramaiah, V. (2020d). "Bi-unitary multiperfect numbers, IV(a)" (PDF). Notes on Number Theory and Discrete Mathematics. 26 (4): 2–32. doi: 10.7546/nntdm.2020.26.4.2-32 .
Haukkanen, Pentti; Sitaramaiah, V. (2021a). "Bi-unitary multiperfect numbers, IV(b)" (PDF). Notes on Number Theory and Discrete Mathematics. 27 (1): 45–69. doi: 10.7546/nntdm.2021.27.1.45-69 .
Haukkanen, Pentti; Sitaramaiah, V. (2021b). "Bi-unitary multiperfect numbers, V" (PDF). Notes on Number Theory and Discrete Mathematics. 27 (2): 20–40. doi: 10.7546/nntdm.2021.27.2.20-40 .
Kishore, Masao (1987). "Odd triperfect numbers are divisible by twelve distinct prime factors". Journal of the Australian Mathematical Society, Series A. 42 (2): 173–182. doi: 10.1017/s1446788700028184 . ISSN 0263-6115. Zbl 0612.10006.
Laatsch, Richard (1986). "Measuring the abundancy of integers". Mathematics Magazine . 59 (2): 84–92. doi:10.2307/2690424. ISSN 0025-570X. JSTOR 2690424. MR 0835144. Zbl 0601.10003.
Merickel, James G. (1999). "Divisors of Sums of Divisors: 10617". The American Mathematical Monthly. 106 (7): 693. doi:10.2307/2589515. JSTOR 2589515. MR 1543520.
Ryan, Richard F. (2003). "A simpler dense proof regarding the abundancy index". Mathematics Magazine. 76 (4): 299–301. doi:10.1080/0025570X.2003.11953197. JSTOR 3219086. MR 1573698. S2CID 120960379.
Sándor, Jozsef; Crstici, Borislav, eds. (2004). Handbook of number theory II . Dordrecht: Kluwer Academic. pp. 32–36. ISBN 1-4020-2546-7. Zbl 1079.11001.
Sándor, József; Mitrinović, Dragoslav S.; Crstici, Borislav, eds. (2006). Handbook of number theory I. Dordrecht: Springer-Verlag. ISBN 1-4020-4215-9. Zbl 1151.11300.
Sorli, Ronald M. (2003). Algorithms in the study of multiperfect and odd perfect numbers (PhD thesis). Sydney: University of Technology. hdl:10453/20034.
Weiner, Paul A. (2000). "The abundancy ratio, a measure of perfection". Mathematics Magazine. 73 (4): 307–310. doi:10.1080/0025570x.2000.11996860. JSTOR 2690980. MR 1573474. S2CID 119773896.

External links

This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.

[fl-1] 1 2 3 4 5 Flammenkamp, Achim. "The Multiply Perfect Numbers Page" . Retrieved 22 January 2014.

[HBI105-2] 1 2 3 Sándor, Mitrinović & Crstici 2006 , p. 105

[3] Dagal, Keneth Adrian P. (2013). "A Lower Bound for τ(n) for k-Multiperfect Number". arXiv: 1309.3527 [math.NT].

[HBI106-4] 1 2 Sándor, Mitrinović & Crstici 2006 , p. 106

[5] Sándor, Mitrinović & Crstici 2006 , pp. 108–109

[HS2020a-6] Haukkanen & Sitaramaiah 2020a

[HS2020b-7] Haukkanen & Sitaramaiah 2020b

[HS2020c-8] Haukkanen & Sitaramaiah 2020c

[HS2020d-9] Haukkanen & Sitaramaiah 2020d

[HS2021a-10] Haukkanen & Sitaramaiah 2021a

[HS2021b-11] Haukkanen & Sitaramaiah 2021b

[1]

[2]

[3]

[4]

[5]

[6]

[7]

[8]

[9]

[10]

[11]

v t e Divisibility-based sets of integers
Overview	Integer factorization Divisor Unitary divisor Divisor function Prime factor Fundamental theorem of arithmetic
Factorization forms	Prime Composite Semiprime Pronic Sphenic Square-free Powerful Perfect power Achilles Smooth Regular Rough Unusual
Constrained divisor sums	Perfect Almost perfect Quasiperfect Multiply perfect Hemiperfect Hyperperfect Superperfect Unitary perfect Semiperfect Practical Descartes Erdős–Nicolas
With many divisors	Abundant Primitive abundant Highly abundant Superabundant Colossally abundant Highly composite Superior highly composite Weird
Aliquot sequence-related	Untouchable Amicable (Triple) Sociable Betrothed
Base-dependent	Equidigital Extravagant Frugal Harshad Polydivisible Smith
Other sets	Arithmetic Deficient Friendly Solitary Sublime Harmonic divisor Refactorable Superperfect