OFFSET
0,4
FORMULA
G.f.: -x^2 + Product_{k>=1} (1 + x^(a(k)*k) / (1 - x^k)).
EXAMPLE
a(0) = a(1) = a(2) = 1: by definition.
a(3) = 2: [2, 1], [1, 1, 1].
a(4) = 3: [2, 2], [2, 1, 1], [1, 1, 1, 1].
a(5) = 3: [2, 2, 1], [2, 1, 1, 1], [1, 1, 1, 1, 1].
a(6) = 5: [3, 3], [2, 2, 2], [2, 2, 1, 1], [2, 1, 1, 1, 1], [1, 1, 1, 1, 1, 1].
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Nov 28 2020
STATUS
approved