OFFSET
1,7
FORMULA
G.f.: Sum_{k>=1} k * x^prime(2*k) / (1 - x^prime(2*k)).
EXAMPLE
a(315) = 3 because 315 = 3^2 * 5 * 7 = prime(2)^2 * prime(3) * prime(4) and (2 + 4) / 2 = 3.
MATHEMATICA
nmax = 100; CoefficientList[Series[Sum[k x^Prime[2 k]/(1 - x^Prime[2 k]), {k, 1, nmax}], {x, 0, nmax}], x] // Rest
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Oct 24 2023
STATUS
approved