OFFSET
0,25
LINKS
Antti Karttunen, Table of n, a(n) for n = 0..1221 (terms 0..200 from Indranil Ghosh)
Eric Weisstein's World of Mathematics, Abundant Number
FORMULA
G.f.: 1/(1 - Sum_{k>=1} x^A005101(k)).
EXAMPLE
a(30) = 3 because we have [30], [18, 12] and [12, 18].
MATHEMATICA
nmax = 95; CoefficientList[Series[1/(1 - Sum[Boole[DivisorSigma[1, k] > 2 k] x^k, {k, 1, nmax}]), {x, 0, nmax}], x]
PROG
(PARI) Vec(1/(1 - sum(k=1, 95, (sigma(k)>2*k)*x^k)) + O(x^95)) \\ Indranil Ghosh, Mar 15 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Feb 18 2017
STATUS
approved