Name First elements Short description OEIS Kolakoski sequence 1, 2, 2, 1, 1, 2, 1, 2, 2, 1, ... The n th term describes the length of the n th run A000002 Euler's totient function φ (n ) 1, 1, 2, 2, 4, 2, 6, 4, 6, 4, ... φ (n ) is the number of positive integers not greater than n that are coprime with n . A000010 Lucas numbers L (n ) 2, 1, 3, 4, 7, 11, 18, 29, 47, 76, ... L (n ) = L (n − 1) + L (n − 2) for n ≥ 2 , with L (0) = 2 and L (1) = 1 . A000032 Prime numbers p n 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, ... The prime numbers p n , with n ≥ 1 . A prime number is a natural number greater than 1 that is not a product of two smaller natural numbers. A000040 Partition numbers P n 1, 1, 2, 3, 5, 7, 11, 15, 22, 30, 42, ... The partition numbers, number of additive breakdowns of n. A000041 Fibonacci numbers F (n ) 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, ... F (n ) = F (n − 1) + F (n − 2) for n ≥ 2 , with F (0) = 0 and F (1) = 1 . A000045 Sylvester's sequence 2, 3, 7, 43, 1807, 3263443, 10650056950807, 113423713055421844361000443, ... a ( n + 1 ) = ∏ k = 0 n a ( k ) + 1 = a ( n ) 2 − a ( n ) + 1 {\displaystyle a(n+1)=\prod _{k=0}^{n}a(k)+1=a(n)^{2}-a(n)+1} for n ≥ 1 , with a (0) = 2 . A000058 Tribonacci numbers 0, 1, 1, 2, 4, 7, 13, 24, 44, 81, ... T (n ) = T (n − 1) + T (n − 2) + T (n − 3) for n ≥ 3 , with T (0) = 0 and T (1) = T (2) = 1 . A000073 Powers of 2 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, ... Powers of 2: 2n for n ≥ 0 A000079 Polyominoes 1, 1, 1, 2, 5, 12, 35, 108, 369, ... The number of free polyominoes with n cells. A000105 Catalan numbers C n 1, 1, 2, 5, 14, 42, 132, 429, 1430, 4862, ... C n = 1 n + 1 ( 2 n n ) = ( 2 n ) ! ( n + 1 ) ! n ! = ∏ k = 2 n n + k k , n ≥ 0. {\displaystyle C_{n}={\frac {1}{n+1}}{2n \choose n}={\frac {(2n)!}{(n+1)!\,n!}}=\prod \limits _{k=2}^{n}{\frac {n+k}{k}},\quad n\geq 0.} A000108 Bell numbers B n 1, 1, 2, 5, 15, 52, 203, 877, 4140, 21147, ... B n is the number of partitions of a set with n elements. A000110 Euler zigzag numbers E n 1, 1, 1, 2, 5, 16, 61, 272, 1385, 7936, ... E n is the number of linear extensions of the "zig-zag" poset. A000111 Lazy caterer's sequence 1, 2, 4, 7, 11, 16, 22, 29, 37, 46, ... The maximal number of pieces formed when slicing a pancake with n cuts. A000124 Pell numbers P n 0, 1, 2, 5, 12, 29, 70, 169, 408, 985, ... a (n ) = 2a (n − 1) + a (n − 2) for n ≥ 2 , with a (0) = 0, a (1) = 1 . A000129 Factorials n ! 1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880, ... n ! = ∏ k = 1 n k {\displaystyle n!=\prod _{k=1}^{n}k} for n ≥ 1 , with 0! = 1 (empty product). A000142 Derangements 1, 0, 1, 2, 9, 44, 265, 1854, 14833, 133496, 1334961, 14684570, 176214841, ... Number of permutations of n elements with no fixed points. A000166 Divisor function σ (n ) 1, 3, 4, 7, 6, 12, 8, 15, 13, 18, 12, 28, ... σ (n ) := σ 1 (n ) is the sum of divisors of a positive integer n . A000203 Fermat numbers F n 3, 5, 17, 257, 65537, 4294967297, 18446744073709551617, 340282366920938463463374607431768211457, ... F n = 2 2 n + 1 for n ≥ 0 . A000215 Polytrees 1, 1, 3, 8, 27, 91, 350, 1376, 5743, 24635, 108968, ... Number of oriented trees with n nodes. A000238 Perfect numbers 6, 28, 496, 8128, 33550336, 8589869056, 137438691328, 2305843008139952128, ... n is equal to the sum s (n ) = σ (n ) − n of the proper divisors of n . A000396 Ramanujan tau function 1, −24, 252, −1472, 4830, −6048, −16744, 84480, −113643, ... Values of the Ramanujan tau function, τ (n ) at n = 1, 2, 3, ... A000594 Landau's function 1, 1, 2, 3, 4, 6, 6, 12, 15, 20, ... The largest order of permutation of n elements. A000793 Narayana's cows 1, 1, 1, 2, 3, 4, 6, 9, 13, 19, ... The number of cows each year if each cow has one cow a year beginning its fourth year. A000930 Padovan sequence 1, 1, 1, 2, 2, 3, 4, 5, 7, 9, ... P (n ) = P (n − 2) + P (n − 3) for n ≥ 3 , with P (0) = P (1) = P (2) = 1 . A000931 Euclid–Mullin sequence 2, 3, 7, 43, 13, 53, 5, 6221671, 38709183810571, 139, ... a (1) = 2; a (n + 1) is smallest prime factor of a (1) a (2) ⋯ a (n ) + 1 . A000945 Lucky numbers 1, 3, 7, 9, 13, 15, 21, 25, 31, 33, ... A natural number in a set that is filtered by a sieve. A000959 Prime powers 2, 3, 4, 5, 7, 8, 9, 11, 13, 16, 17, 19, ... Positive integer powers of prime numbers A000961 Central binomial coefficients 1, 2, 6, 20, 70, 252, 924, ... ( 2 n n ) = ( 2 n ) ! ( n ! ) 2 for all n ≥ 0 {\displaystyle {2n \choose n}={\frac {(2n)!}{(n!)^{2}}}{\text{ for all }}n\geq 0} , numbers in the center of even rows of Pascal's triangle A000984 Motzkin numbers 1, 1, 2, 4, 9, 21, 51, 127, 323, 835, ... The number of ways of drawing any number of nonintersecting chords joining n (labeled) points on a circle. A001006 Jordan–Pólya numbers 1, 2, 4, 6, 8, 12, 16, 24, 32, 36, 48, 64, ... Numbers that are the product of factorials. A001013 Jacobsthal numbers 0, 1, 1, 3, 5, 11, 21, 43, 85, 171, 341, ... a (n ) = a (n − 1) + 2a (n − 2) for n ≥ 2 , with a (0) = 0, a (1) = 1 . A001045 Sum of proper divisors s (n ) 0, 1, 1, 3, 1, 6, 1, 7, 4, 8, ... s (n ) = σ (n ) − n is the sum of the proper divisors of the positive integer n . A001065 Wedderburn–Etherington numbers 0, 1, 1, 1, 2, 3, 6, 11, 23, 46, ... The number of binary rooted trees (every node has out-degree 0 or 2) with n endpoints (and 2n − 1 nodes in all). A001190 Gould's sequence 1, 2, 2, 4, 2, 4, 4, 8, 2, 4, 4, 8, 4, 8, 8, ... Number of odd entries in row n of Pascal's triangle. A001316 Semiprimes 4, 6, 9, 10, 14, 15, 21, 22, 25, 26, ... Products of two primes, not necessarily distinct. A001358 Golomb sequence 1, 2, 2, 3, 3, 4, 4, 4, 5, 5, ... a (n ) is the number of times n occurs, starting with a (1) = 1 . A001462 Perrin numbers P n 3, 0, 2, 3, 2, 5, 5, 7, 10, 12, ... P (n ) = P (n − 2) + P (n − 3) for n ≥ 3 , with P (0) = 3, P (1) = 0, P (2) = 2 . A001608 Sorting number 0, 1, 3, 5, 8, 11, 14, 17, 21, 25, 29, 33, 37, 41, 45, 49, ... Used in the analysis of comparison sorts . A001855 Cullen numbers C n 1, 3, 9, 25, 65, 161, 385, 897, 2049, 4609, 10241, 22529, 49153, 106497, ... C n = n ⋅ 2n + 1 , with n ≥ 0 . A002064 Primorials p n # 1, 2, 6, 30, 210, 2310, 30030, 510510, 9699690, 223092870, ... p n # , the product of the first n primes. A002110 Highly composite numbers 1, 2, 4, 6, 12, 24, 36, 48, 60, 120, ... A positive integer with more divisors than any smaller positive integer. A002182 Superior highly composite numbers 2, 6, 12, 60, 120, 360, 2520, 5040, 55440, 720720, ... A positive integer n for which there is an e > 0 such that d (n )/ n e ≥ d (k )/ k e for all k > 1 . A002201 Pronic numbers 0, 2, 6, 12, 20, 30, 42, 56, 72, 90, ... a (n ) = 2t (n ) = n (n + 1) , with n ≥ 0 where t (n ) are the triangular numbers. A002378 Markov numbers 1, 2, 5, 13, 29, 34, 89, 169, 194, ... Positive integer solutions of x 2 + y 2 + z 2 = 3xyz . A002559 Composite numbers 4, 6, 8, 9, 10, 12, 14, 15, 16, 18, ... The numbers n of the form xy for x > 1 and y > 1 . A002808 Ulam number 1, 2, 3, 4, 6, 8, 11, 13, 16, 18, ... a (1) = 1; a (2) = 2; for n > 2, a (n ) is least number > a (n − 1) which is a unique sum of two distinct earlier terms; semiperfect. A002858 Prime knots 0, 0, 1, 1, 2, 3, 7, 21, 49, 165, 552, 2176, 9988, ... The number of prime knots with n crossings. A002863 Carmichael numbers 561, 1105, 1729, 2465, 2821, 6601, 8911, 10585, 15841, 29341, ... Composite numbers n such that a n − 1 ≡ 1 (mod n ) if a is coprime with n . A002997 Woodall numbers 1, 7, 23, 63, 159, 383, 895, 2047, 4607, ... n ⋅ 2n − 1 , with n ≥ 1 . A003261 Arithmetic numbers 1, 3, 5, 6, 7, 11, 13, 14, 15, 17, 19, 20, 21, 22, 23, 27, ... An integer for which the average of its positive divisors is also an integer. A003601 Colossally abundant numbers 2, 6, 12, 60, 120, 360, 2520, 5040, 55440, 720720, ... A number n is colossally abundant if there is an ε > 0 such that for all k > 1 , σ ( n ) n 1 + ε ≥ σ ( k ) k 1 + ε , {\displaystyle {\frac {\sigma (n)}{n^{1+\varepsilon }}}\geq {\frac {\sigma (k)}{k^{1+\varepsilon }}},} where σ denotes the sum-of-divisors function.
A004490 Alcuin's sequence 0, 0, 0, 1, 0, 1, 1, 2, 1, 3, 2, 4, 3, 5, 4, 7, 5, 8, 7, 10, 8, 12, 10, 14, ... Number of triangles with integer sides and perimeter n . A005044 Deficient numbers 1, 2, 3, 4, 5, 7, 8, 9, 10, 11, ... Positive integers n such that σ (n ) < 2n . A005100 Abundant numbers 12, 18, 20, 24, 30, 36, 40, 42, 48, 54, ... Positive integers n such that σ (n ) > 2n . A005101 Untouchable numbers 2, 5, 52, 88, 96, 120, 124, 146, 162, 188, ... Cannot be expressed as the sum of all the proper divisors of any positive integer. A005114 Recamán's sequence 0, 1, 3, 6, 2, 7, 13, 20, 12, 21, 11, 22, 10, 23, 9, 24, 8, 25, 43, 62, ... "subtract if possible, otherwise add" : a (0) = 0; for n > 0, a (n ) = a (n − 1) − n if that number is positive and not already in the sequence, otherwise a (n ) = a (n − 1) + n , whether or not that number is already in the sequence. A005132 Look-and-say sequence 1, 11, 21, 1211, 111221, 312211, 13112221, 1113213211, 31131211131221, 13211311123113112211, ... A = 'frequency' followed by 'digit'-indication. A005150 Practical numbers 1, 2, 4, 6, 8, 12, 16, 18, 20, 24, 28, 30, 32, 36, 40, ... All smaller positive integers can be represented as sums of distinct factors of the number. A005153 Alternating factorial 1, 1, 5, 19, 101, 619, 4421, 35899, 326981, 3301819, 36614981, 442386619, 5784634181, 81393657019, ... ∑ k = 0 n − 1 ( − 1 ) k ( n − k ) ! {\displaystyle \sum _{k=0}^{n-1}(-1)^{k}(n-k)!} A005165 Fortunate numbers 3, 5, 7, 13, 23, 17, 19, 23, 37, 61, ... The smallest integer m > 1 such that p n # + m is a prime number, where the primorial p n # is the product of the first n prime numbers. A005235 Semiperfect numbers 6, 12, 18, 20, 24, 28, 30, 36, 40, 42, ... A natural number n that is equal to the sum of all or some of its proper divisors. A005835 Magic constants 15, 34, 65, 111, 175, 260, 369, 505, 671, 870, 1105, 1379, 1695, 2056, ... Sum of numbers in any row, column, or diagonal of a magic square of order n ≥ 3 . A006003 Weird numbers 70, 836, 4030, 5830, 7192, 7912, 9272, 10430, 10570, 10792, ... A natural number that is abundant but not semiperfect. A006037 Farey sequence numerators 0, 1, 0, 1, 1, 0, 1, 1, 2, 1, ... A006842 Farey sequence denominators 1, 1, 1, 2, 1, 1, 3, 2, 3, 1, ... A006843 Euclid numbers 2, 3, 7, 31, 211, 2311, 30031, 510511, 9699691, 223092871, ... p n # + 1 , i.e. 1 + product of first n consecutive primes. A006862 Kaprekar numbers 1, 9, 45, 55, 99, 297, 703, 999, 2223, 2728, ... X 2 = Ab n + B , where 0 < B < b n and X = A + B . A006886 Sphenic numbers 30, 42, 66, 70, 78, 102, 105, 110, 114, 130, ... Products of 3 distinct primes. A007304 Giuga numbers 30, 858, 1722, 66198, 2214408306, ... Composite numbers so that for each of its distinct prime factors p i we have p i 2 | ( n − p i ) {\displaystyle p_{i}^{2}\,|\,(n-p_{i})} . A007850 Radical of an integer 1, 2, 3, 2, 5, 6, 7, 2, 3, 10, ... The radical of a positive integer n is the product of the distinct prime numbers dividing n . A007947 Thue–Morse sequence 0, 1, 1, 0, 1, 0, 0, 1, 1, 0, ... A010060 Regular paperfolding sequence 1, 1, 0, 1, 1, 0, 0, 1, 1, 1, ... At each stage an alternating sequence of 1s and 0s is inserted between the terms of the previous sequence. A014577 Blum integers 21, 33, 57, 69, 77, 93, 129, 133, 141, 161, 177, ... Numbers of the form pq where p and q are distinct primes congruent to 3 (mod 4) . A016105 Magic numbers 2, 8, 20, 28, 50, 82, 126, ... A number of nucleons (either protons or neutrons ) such that they are arranged into complete shells within the atomic nucleus . A018226 Superperfect numbers 2, 4, 16, 64, 4096, 65536, 262144, 1073741824, 1152921504606846976, 309485009821345068724781056, ... Positive integers n for which σ 2 (n ) = σ (σ (n )) = 2n . A019279 Bernoulli numbers B n 1, −1, 1, 0, −1, 0, 1, 0, −1, 0, 5, 0, −691, 0, 7, 0, −3617, 0, 43867, 0, ... A027641 Hyperperfect numbers 6, 21, 28, 301, 325, 496, 697, ... k -hyperperfect numbers, i.e. n for which the equality n = 1 + k (σ (n ) − n − 1) holds. A034897 Achilles numbers 72, 108, 200, 288, 392, 432, 500, 648, 675, 800, ... Positive integers which are powerful but imperfect. A052486 Primary pseudoperfect numbers 2, 6, 42, 1806, 47058, 2214502422, 52495396602, ... Satisfies a certain Egyptian fraction . A054377 Erdős–Woods numbers 16, 22, 34, 36, 46, 56, 64, 66, 70, 76, 78, 86, 88, ... The length of an interval of consecutive integers with property that every element has a factor in common with one of the endpoints. A059756 Sierpinski numbers 78557, 271129, 271577, 322523, 327739, 482719, 575041, 603713, 903983, 934909, ... Odd k for which { k ⋅ 2n + 1 : n ∈ N {\displaystyle \mathbb {N} } } consists only of composite numbers. A076336 Riesel numbers 509203, 762701, 777149, 790841, 992077, ... Odd k for which { k ⋅ 2n − 1 : n ∈ N {\displaystyle \mathbb {N} } } consists only of composite numbers. A076337 Baum–Sweet sequence 1, 1, 0, 1, 1, 0, 0, 1, 0, 1, ... a (n ) = 1 if the binary representation of n contains no block of consecutive zeros of odd length; otherwise a (n ) = 0 . A086747 Gijswijt's sequence 1, 1, 2, 1, 1, 2, 2, 2, 3, 1, ... The n th term counts the maximal number of repeated blocks at the end of the subsequence from 1 to n −1 A090822 Carol numbers −1, 7, 47, 223, 959, 3967, 16127, 65023, 261119, 1046527, ... a ( n ) = ( 2 n − 1 ) 2 − 2. {\displaystyle a(n)=(2^{n}-1)^{2}-2.} A093112 Juggler sequence 0, 1, 1, 5, 2, 11, 2, 18, 2, 27, ... If n ≡ 0 (mod 2) then ⌊√ n ⌋ else ⌊n 3/2 ⌋ . A094683 Highly totient numbers 1, 2, 4, 8, 12, 24, 48, 72, 144, 240, ... Each number k on this list has more solutions to the equation φ (x ) = k than any preceding k . A097942 Euler numbers 1, 0, −1, 0, 5, 0, −61, 0, 1385, 0, ... 1 cosh t = 2 e t + e − t = ∑ n = 0 ∞ E n n ! ⋅ t n . {\displaystyle {\frac {1}{\cosh t}}={\frac {2}{e^{t}+e^{-t}}}=\sum _{n=0}^{\infty }{\frac {E_{n}}{n!}}\cdot t^{n}.} A122045 Polite numbers 3, 5, 6, 7, 9, 10, 11, 12, 13, 14, 15, 17, ... A positive integer that can be written as the sum of two or more consecutive positive integers. A138591 Erdős–Nicolas numbers 24, 2016, 8190, 42336, 45864, 392448, 714240, 1571328, ... A number n such that there exists another number m and ∑ d ∣ n , d ≤ m d = n . {\displaystyle \sum _{d\mid n,\ d\leq m}\!d=n.} A194472 Solution to Stepping Stone Puzzle 1, 16, 28, 38, 49, 60, ... The maximal value a (n ) of the stepping stone puzzle A337663