A008439 - OEIS

A008439

Expansion of Jacobi theta constant theta_2^5 /32.

1, 5, 10, 15, 25, 31, 35, 55, 60, 60, 90, 90, 95, 135, 125, 126, 170, 180, 175, 215, 220, 195, 285, 280, 245, 340, 300, 320, 405, 350, 351, 450, 465, 415, 515, 480, 425, 620, 590, 505, 655, 625, 590, 755, 660, 650, 805, 770, 755, 855, 841, 730, 1045, 960, 770, 1100

(list; graph; refs; listen; history; text; internal format)

OFFSET

0,2

COMMENTS

Also number of ways of writing n as a sum of five triangular numbers. - N. J. A. Sloane, Jun 01 2013

REFERENCES

J. H. Conway and N. J. A. Sloane, "Sphere Packings, Lattices and Groups", Springer-Verlag, p. 102.

LINKS

Seiichi Manyama, Table of n, a(n) for n = 0..10000

K. Ono, S. Robins and P. T. Wahl, On the representation of integers as sums of triangular numbers, Aequationes mathematicae, August 1995, Volume 50, Issue 1-2, pp 73-94.

FORMULA

a(0) = 1, a(n) = (5/n)*Sum_{k=1..n} A002129(k)*a(n-k) for n > 0. - Seiichi Manyama, May 06 2017

G.f.: exp(Sum_{k>=1} 5*(x^k/k)/(1 + x^k)). - Ilya Gutkovskiy, Jul 31 2017

MATHEMATICA

a002129[n_]:=-Sum[(-1)^d*d, {d, Divisors[n]}]; a[n_]:=a[n]=If[n==0, 1, 5 Sum[a002129[k] a[n - k], {k, n}]/n]; Table[a[n], {n, 0, 100}] (* Indranil Ghosh, Aug 02 2017 *)

CROSSREFS

Number of ways of writing n as a sum of k triangular numbers, for k=1,...: A010054, A008441, A008443, A008438, A008439, A008440, A226252, A007331, A226253, A226254, A226255, A014787, A014809.

Sequence in context: A313817 A344294 A151761 * A276514 A340961 A031471

Adjacent sequences: A008436 A008437 A008438 * A008440 A008441 A008442

KEYWORD

nonn

AUTHOR

N. J. A. Sloane

EXTENSIONS

More terms from Seiichi Manyama, May 05 2017

STATUS

approved