OFFSET
1,4
FORMULA
a(n) = [x^n] Product_{d|n} (1 + x^(2*d) / (1 - x^d)).
EXAMPLE
a(15) = 7 because we have [5, 5, 5], [3, 3, 3, 3, 3], [5, 5, 1, 1, 1, 1, 1], [3, 3, 3, 3, 1, 1, 1], [3, 3, 3, 1, 1, 1, 1, 1, 1], [3, 3, 1, 1, 1, 1, 1, 1, 1, 1, 1] and [1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1].
MATHEMATICA
Table[SeriesCoefficient[Product[1 + x^(2 d)/(1 - x^d), {d, Divisors[n]}], {x, 0, n}], {n, 1, 70}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Nov 28 2020
STATUS
approved