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A284641 Expansion of (Sum_{k>=0} x^(k^2*(k+1)^2/4))^12. 1
1, 12, 66, 220, 495, 792, 924, 792, 495, 232, 198, 672, 1981, 3960, 5544, 5544, 3960, 1980, 726, 792, 2982, 7920, 13860, 16632, 13860, 7920, 2970, 880, 2046, 7920, 18480, 27720, 27720, 18480, 7920, 1980, 727, 4092, 14520, 29700, 38610, 33264, 19404, 7920, 2475, 1584, 6996, 22584, 43560, 55440, 49896 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Number of ways to write n as an ordered sum of 12 squares of triangular numbers (A000537).

Every number is the sum of three triangular numbers (Fermat's polygonal number theorem).

Conjecture: a(n) > 0 for all n.

Extended conjecture: every number is the sum of at most 12 squares of triangular numbers (or partial sums of cubes).

Is there a solution, in analogy with Waring's problem (see A002804), for the partial sums of k-th powers?

LINKS

Table of n, a(n) for n=0..50.

Ilya Gutkovskiy, Extended graphical example

Index to sequences related to polygonal numbers

FORMULA

G.f.: (Sum_{k>=0} x^(k^2*(k+1)^2/4))^12.

MATHEMATICA

nmax = 50; CoefficientList[Series[Sum[x^(k^2 (k + 1)^2/4), {k, 0, nmax}]^12, {x, 0, nmax}], x]

CROSSREFS

Cf. A000217, A000537, A014787, A282173, A282288.

Sequence in context: A001490 A010928 A080559 * A226235 A045853 A277104

Adjacent sequences:  A284638 A284639 A284640 * A284642 A284643 A284644

KEYWORD

nonn

AUTHOR

Ilya Gutkovskiy, May 06 2017

STATUS

approved

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Last modified October 15 16:01 EDT 2018. Contains 316236 sequences. (Running on oeis4.)