OFFSET
0,37
LINKS
Eric Weisstein's World of Mathematics, Composite Number
FORMULA
G.f.: ((1 + x^2)/(1 + x))*Product_{k>=1} (1 + x^k)/((1 + x^(2*k))*(1 + x^prime(k))).
EXAMPLE
a(48) = 3 because we have [39, 9], [33, 15] and [27, 21].
MATHEMATICA
nmax = 105; CoefficientList[Series[(1 + x^2)/(1 + x) Product[(1 + x^k)/((1 + x^(2 k)) (1 + x^Prime[k])), {k, 1, nmax}], {x, 0, nmax}], x]
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Dec 31 2016
STATUS
approved