OFFSET
0,7
LINKS
Eric Weisstein's World of Mathematics, Multiplicative Perfect Number
FORMULA
G.f.: 1/(1 - Sum_{k>=1} x^A007422(k)).
EXAMPLE
a(8) = 5 because we have [8], [6, 1, 1], [1, 6, 1], [1, 1, 6] and [1, 1, 1, 1, 1, 1, 1, 1].
MATHEMATICA
nmax = 52; CoefficientList[Series[1/(1 - Sum[Boole[Sqrt[k]^DivisorSigma[0, k]/k == k] x^k, {k, 1, nmax}]), {x, 0, nmax}], x]
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Feb 18 2017
STATUS
approved