OFFSET
1,2
COMMENTS
Reversion of g.f. (with constant term omitted) for A000219.
LINKS
N. J. A. Sloane, Transforms
Eric Weisstein's World of Mathematics, Series Reversion
FORMULA
G.f. A(x) satisfies: -1 + Product_{k>=1} 1/(1 - A(x)^k)^k = x.
MATHEMATICA
nmax = 24; Rest[CoefficientList[InverseSeries[Series[-1 + Product[1/(1 - x^k)^k, {k, 1, nmax}], {x, 0, nmax}], x], x]]
nmax = 24; Rest[CoefficientList[InverseSeries[Series[-1 + Exp[Sum[DivisorSigma[2, k] x^k/k, {k, 1, nmax}]], {x, 0, nmax}], x], x]]
CROSSREFS
KEYWORD
sign
AUTHOR
Ilya Gutkovskiy, Aug 24 2017
STATUS
approved