Seventh power

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In arithmetic and algebra the seventh power of a number n is the result of multiplying seven instances of n together. So:

Contents

n7 = n × n × n × n × n × n × n.

Seventh powers are also formed by multiplying a number by its sixth power, the square of a number by its fifth power, or the cube of a number by its fourth power.

The sequence of seventh powers of integers is:

0, 1, 128, 2187, 16384, 78125, 279936, 823543, 2097152, 4782969, 10000000, 19487171, 35831808, 62748517, 105413504, 170859375, 268435456, 410338673, 612220032, 893871739, 1280000000, 1801088541, 2494357888, 3404825447, 4586471424, 6103515625, 8031810176, ... (sequence A001015 in the OEIS )

In the archaic notation of Robert Recorde, the seventh power of a number was called the "second sursolid". [1]

Properties

Leonard Eugene Dickson studied generalizations of Waring's problem for seventh powers, showing that every non-negative integer can be represented as a sum of at most 258 non-negative seventh powers [2] (17 is 1, and 27 is 128). All but finitely many positive integers can be expressed more simply as the sum of at most 46 seventh powers. [3] If powers of negative integers are allowed, only 12 powers are required. [4]

The smallest number that can be represented in two different ways as a sum of four positive seventh powers is 2056364173794800. [5]

The smallest seventh power that can be represented as a sum of eight distinct seventh powers is: [6]

The two known examples of a seventh power expressible as the sum of seven seventh powers are

(M. Dodrill, 1999); [7]

and

(Maurice Blondot, 11/14/2000); [7]

any example with fewer terms in the sum would be a counterexample to Euler's sum of powers conjecture, which is currently only known to be false for the powers 4 and 5.

See also

Related Research Articles

Euler's conjecture is a disproved conjecture in mathematics related to Fermat's Last Theorem. It was proposed by Leonhard Euler in 1769. It states that for all integers n and k greater than 1, if the sum of n many kth powers of positive integers is itself a kth power, then n is greater than or equal to k:

In mathematics, the factorial of a non-negative integer , denoted by , is the product of all positive integers less than or equal to . The factorial of also equals the product of with the next smaller factorial:

In number theory, integer factorization is the decomposition of a composite number into a product of smaller integers. If these factors are further restricted to prime numbers, the process is called prime factorization.

<span class="mw-page-title-main">Prime number</span> Evenly divided only by 1 or itself

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<span class="mw-page-title-main">Perfect number</span> Integer equal to the sum of its proper divisors

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In number theory, Waring's problem asks whether each natural number k has an associated positive integer s such that every natural number is the sum of at most s natural numbers raised to the power k. For example, every natural number is the sum of at most 4 squares, 9 cubes, or 19 fourth powers. Waring's problem was proposed in 1770 by Edward Waring, after whom it is named. Its affirmative answer, known as the Hilbert–Waring theorem, was provided by Hilbert in 1909. Waring's problem has its own Mathematics Subject Classification, 11P05, "Waring's problem and variants".

<span class="mw-page-title-main">Exponentiation</span> Mathematical operation

Exponentiation is a mathematical operation, written as bn, involving two numbers, the baseb and the exponent or powern, and pronounced as "b (raised) to the n". When n is a positive integer, exponentiation corresponds to repeated multiplication of the base: that is, bn is the product of multiplying n bases:

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<span class="mw-page-title-main">Cube (algebra)</span> Number raised to the third power

In arithmetic and algebra, the cube of a number n is its third power, that is, the result of multiplying three instances of n together. The cube of a number or any other mathematical expression is denoted by a superscript 3, for example 23 = 8 or (x + 1)3.

<span class="mw-page-title-main">Square (algebra)</span> Result of multiplying a number, or other expression, by itself

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In arithmetic and algebra, the fourth power of a number n is the result of multiplying four instances of n together. So:

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<span class="mw-page-title-main">Perfect power</span> Positive integer that is an integer power of another positive integer

In mathematics, a perfect power is a natural number that is a product of equal natural factors, or, in other words, an integer that can be expressed as a square or a higher integer power of another integer greater than one. More formally, n is a perfect power if there exist natural numbers m > 1, and k > 1 such that mk = n. In this case, n may be called a perfect kth power. If k = 2 or k = 3, then n is called a perfect square or perfect cube, respectively. Sometimes 0 and 1 are also considered perfect powers.

<span class="mw-page-title-main">Polite number</span>

In number theory, a polite number is a positive integer that can be written as the sum of two or more consecutive positive integers. A positive integer which is not polite is called impolite. The impolite numbers are exactly the powers of two, and the polite numbers are the natural numbers that are not powers of two.

In mathematics and statistics, sums of powers occur in a number of contexts:

In arithmetic and algebra, the fifth power or sursolid of a number n is the result of multiplying five instances of n together:

In arithmetic and algebra the sixth power of a number n is the result of multiplying six instances of n together. So:

<span class="mw-page-title-main">Sums of three cubes</span> Problem in number theory

In the mathematics of sums of powers, it is an open problem to characterize the numbers that can be expressed as a sum of three cubes of integers, allowing both positive and negative cubes in the sum. A necessary condition for to equal such a sum is that cannot equal 4 or 5 modulo 9, because the cubes modulo 9 are 0, 1, and −1, and no three of these numbers can sum to 4 or 5 modulo 9. It is unknown whether this necessary condition is sufficient.

In arithmetic and algebra the eighth power of a number n is the result of multiplying eight instances of n together. So:

In mathematics, the fibbinary numbers are the numbers whose binary representation does not contain two consecutive ones. That is, they are sums of distinct and non-consecutive powers of two.

References

  1. Womack, D. (2015), "Beyond tetration operations: their past, present and future", Mathematics in School, 44 (1): 23–26[ dead link ]
  2. Dickson, L. E. (1934), "A new method for universal Waring theorems with details for seventh powers", American Mathematical Monthly, 41 (9): 547–555, doi:10.2307/2301430, JSTOR   2301430, MR   1523212
  3. Kumchev, Angel V. (2005), "On the Waring-Goldbach problem for seventh powers", Proceedings of the American Mathematical Society, 133 (10): 2927–2937, doi: 10.1090/S0002-9939-05-07908-6 , MR   2159771
  4. Choudhry, Ajai (2000), "On sums of seventh powers", Journal of Number Theory, 81 (2): 266–269, doi: 10.1006/jnth.1999.2465 , MR   1752254
  5. Ekl, Randy L. (1996), "Equal sums of four seventh powers", Mathematics of Computation, 65 (216): 1755–1756, Bibcode:1996MaCom..65.1755E, doi: 10.1090/S0025-5718-96-00768-5 , MR   1361807
  6. Stewart, Ian (1989), Game, set, and math: Enigmas and conundrums, Basil Blackwell, Oxford, p. 123, ISBN   0-631-17114-2, MR   1253983
  7. 1 2 Quoted in Meyrignac, Jean-Charles (14 February 2001). "Computing Minimal Equal Sums Of Like Powers: Best Known Solutions" . Retrieved 17 July 2017.