OFFSET
1,22
COMMENTS
Number of ways to write n as the difference of two pentagonal numbers.
FORMULA
G.f.: Sum_{i>=0} Sum_{j>=i} Product_{k=i..j} x^(3*k + 1).
MATHEMATICA
nmax = 92; CoefficientList[Series[Sum[x^(k (3 k - 1)/2)/(1 - x^(3 k)), {k, 1, nmax}], {x, 0, nmax}], x] // Rest
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Apr 06 2020
STATUS
approved