OFFSET
0,6
FORMULA
a(n) = [x^n] 1/(1 - Sum_{bigomega(k) = bigomega(n)} x^k).
EXAMPLE
a(20) = 3 because we have [20], [12, 8] and [8, 12], where 20, 12 and 8 are numbers that are the product of exactly 3 (not necessarily distinct) primes.
MATHEMATICA
Table[SeriesCoefficient[1/(1 - Sum[Boole[PrimeOmega[k] == PrimeOmega[n]] x^k, {k, 1, n}]), {x, 0, n}], {n, 0, 62}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Mar 18 2018
STATUS
approved