A093518 Number of ways of representing n as exactly 2 generalized pentagonal numbers.

1, 1, 2, 1, 1, 1, 1, 2, 1, 1, 1, 0, 2, 1, 2, 1, 1, 2, 0, 1, 1, 0, 2, 1, 2, 0, 1, 3, 1, 1, 1, 1, 0, 1, 1, 1, 1, 2, 1, 0, 2, 2, 2, 0, 1, 1, 0, 2, 1, 0, 1, 1, 3, 1, 0, 1, 1, 2, 2, 1, 0, 1, 2, 1, 1, 0, 2, 0, 0, 1, 2, 1, 2, 1, 0, 2, 0, 3, 1, 2, 1, 0, 2, 1, 1, 1, 1, 0, 0, 1, 0, 1, 4, 1, 1, 0, 1, 2, 0, 2, 1, 1, 2, 1

Offset

0,3

Links

Table of n, a(n) for n=0..103.

Example

a(7)=2 as we have 7+0=5+2

Prog

(PARI) { v=vector(101); v[1]=0; for (i=1, 50, v[2*i]=i*(3*i-1)/2; v[2*i+1]=i*(3*i+1)/2); x=vector(500); for (a=1, 50, for (b=a, 50, if (v[a]+v[b]<500, x[v[a]+v[b]+1]++))); x }

Crossrefs

Cf. A001318 (generalized pentagonal numbers), A002107 (expansion of Product (1-x^k)^2, k=1..inf.), A093519 (A093518(n)=0).

Sequence in context: A238988 A261013 A335106 * A128184 A373244 A025450

Adjacent sequences: A093515 A093516 A093517 * A093519 A093520 A093521

Keyword

nonn

Author

Jon Perry, Mar 29 2004

Status

approved