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A280618
Expansion of (Sum_{k>=1} x^(k^3))^2.
12
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
OFFSET
0,10
COMMENTS
Number of ways to write n as an ordered sum of two positive cubes.
LINKS
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
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Jan 06 2017
STATUS
approved