OFFSET
0,2
LINKS
Vaclav Kotesovec, Table of n, a(n) for n = 0..10000
FORMULA
G.f.: exp(-2*Sum_{j>=1} Sum_{k>=1} k^j*x^(j*k)/j). - Ilya Gutkovskiy, Feb 07 2018
MATHEMATICA
nmax = 50; poly = ConstantArray[0, nmax+1]; poly[[1]] = 1; poly[[2]] = -2; poly[[3]] = 1; Do[Do[Do[poly[[j+1]] -= k*poly[[j-k+1]], {j, nmax, k, -1}]; , {p, 1, 2}], {k, 2, nmax}]; poly (* Vaclav Kotesovec, Jan 07 2016 *)
With[{nmax = 50}, CoefficientList[Series[Product[(1 - k*q^k)^2, {k, 1, nmax}], {q, 0, nmax}], q]] (* G. C. Greubel, Feb 18 2018 *)
PROG
(PARI) m=50; q='q+O('q^m); Vec(prod(n=1, m, (1-n*q^n)^2)) \\ G. C. Greubel, Feb 18 2018
(Magma) Coefficients(&*[(1-m*x^m)^2:m in [1..40]])[1..40] where x is PolynomialRing(Integers()).1; // G. C. Greubel, Feb 18 2018
CROSSREFS
KEYWORD
sign
AUTHOR
STATUS
approved