OFFSET
0,6
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..445
FORMULA
E.g.f.: Product_{i>=1} (1-x^i)^(1/i).
EXAMPLE
G.f. = 1 - x - x^2 + x^3 - x^4 + 41*x^5 - 131*x^6 + 1499*x^7 - 4159*x^8 + ...
MATHEMATICA
nmax = 50; CoefficientList[Series[Product[(1 - x^k)^(1/k), {k, 1, nmax}], {x, 0, nmax}], x]*Range[0, nmax]! (* G. C. Greubel, Nov 24 2016 *)
a[ n_] := If[n < 0, 0, n! SeriesCoefficient[ Exp[ -Sum[DivisorSigma[0, k] x^k/k, {k, n}]], {x, 0, n}]]; (* Michael Somos, Nov 25 2016 *)
CROSSREFS
KEYWORD
sign
AUTHOR
STATUS
approved