

A097811


Numbers n such that n^3 is the sum of three or more consecutive positive cubes.


4



6, 20, 40, 60, 70, 180, 330, 540, 1155, 1581, 2805, 2856, 3876, 5544, 16830, 27060, 62244, 82680, 90090, 175440, 237456, 249424, 273819, 413820, 431548, 534660, 860706, 1074744, 1205750, 1306620, 1630200, 1764070, 1962820, 1983150
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OFFSET

1,1


COMMENTS

These numbers were found by exhaustive search. The sums are not unique; for n=2856, there are two representations. The Mathematica code prints n, the range of cubes in the sum and the number of cubes in the sum. For instance, 82680^3 equals the sum of 6591 cubes! A faster program was used to check all sums s of consecutive cubes such that s < 2000000^3.
2856^3 is the only cube < 2*10^23 that is a sum in two different ways. 2856^3 = 213^3 +...+ 555^3 = 273^3 +...+ 560^3.  Donovan Johnson, Feb 22 2011
The terms of this sequence tend to contain only small primes. Is a(n)^(1/3) an upper bound for the largest prime factor of a(n)?  Ralf Stephan, May 22 2013
Note that by Fermat's theorem no cube is the sum of two positive cubes.
The cubes of the terms form a subsequence of A265845 (numbers that are sums of consecutive positive cubes in more than one way) which is sparse: among the first 1000 terms of A265845, only 17 are cubes.  Jonathan Sondow, Jan 10 2016


LINKS

Chai Wah Wu, Table of n, a(n) for n = 1..68 (terms n = 1..55 from Donovan Johnson)
K. S. Brown, Sum of Consecutive Nth Powers Equals an Nth Power


FORMULA

a(n) = A131643(n)^(1/3).  Jonathan Sondow, Jan 10 2016


EXAMPLE

20 is in this sequence because 11^3 + 12^3 + 13^3 + 14^3 = 20^3.


MATHEMATICA

g[m0_, m1_] := (m1m0+1)(m0+m1)(m0^2+m1^2+m1m0)/4; lst={}; Do[n=g[m0, m1]^(1/3); If[IntegerQ[n], Print[{n, m0, m1, m1m0+1}]; AppendTo[lst, n]], {m1, 2, 14000}, {m0, m11, 1, 1}]; Union[lst]


CROSSREFS

Cf. A097812 (n^2 is the sum of consecutive squares), A265845.
See A131643 for the actual cubes.
Sequence in context: A106528 A031068 A031052 * A143711 A077539 A002943
Adjacent sequences: A097808 A097809 A097810 * A097812 A097813 A097814


KEYWORD

nonn


AUTHOR

T. D. Noe, Aug 25 2004; Sep 07 2004


EXTENSIONS

Name edited by Altug Alkan, Dec 07 2015


STATUS

approved



