A280618 - OEIS

A280618

Expansion of (Sum_{k>=1} x^(k^3))^2.

0, 0, 1, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0

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OFFSET

0,10

COMMENTS

Number of ways to write n as an ordered sum of two positive cubes.

LINKS

Antti Karttunen, Table of n, a(n) for n = 0..65537

Eric Weisstein's World of Mathematics, Cubic Number

Index entries for sequences related to sums of cubes

FORMULA

G.f.: (Sum_{k>=1} x^(k^3))^2.

EXAMPLE

a(9) = 2 because we have [8, 1] and [1, 8].

MATHEMATICA

nmax = 150; CoefficientList[Series[(Sum[x^(k^3), {k, 1, nmax}])^2, {x, 0, nmax}], x]

PROG

(PARI)

A010057(n) = ispower(n, 3);

A280618(n) = if(n<2, 0, sum(r=1, sqrtnint(n-1, 3), A010057(n-(r^3)))); \\ Antti Karttunen, Nov 30 2021

CROSSREFS

Cf. A000578, A001235 (positions of terms > 3), A003325 (of nonzero terms), A010057, A063725, A173677.

Sequence in context: A060478 A088806 A359602 * A347714 A089807 A089810

Adjacent sequences: A280615 A280616 A280617 * A280619 A280620 A280621

KEYWORD

nonn

AUTHOR

Ilya Gutkovskiy, Jan 06 2017

STATUS

approved

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