OFFSET
0,3
COMMENTS
Invert transform of A001157.
LINKS
Seiichi Manyama, Table of n, a(n) for n = 0..1754
N. J. A. Sloane, Transforms
FORMULA
G.f.: 1/(1 + x * (d/dx) log(Product_{k>=1} (1 - x^k)^k)).
a(0) = 1; a(n) = Sum_{k=1..n} sigma_2(k)*a(n-k).
MAPLE
a:=series(1/(1-add(k^2*x^k/(1-x^k), k=1..100)), x=0, 27): seq(coeff(a, x, n), n=0..26); # Paolo P. Lava, Apr 02 2019
MATHEMATICA
nmax = 26; CoefficientList[Series[1/(1 - Sum[k^2 x^k/(1 - x^k), {k, 1, nmax}]), {x, 0, nmax}], x]
nmax = 26; CoefficientList[Series[1/(1 + x D[Log[Product[(1 - x^k)^k, {k, 1, nmax}]], x]), {x, 0, nmax}], x]
a[0] = 1; a[n_] := a[n] = Sum[DivisorSigma[2, k] a[n - k], {k, 1, n}]; Table[a[n], {n, 0, 26}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Oct 18 2018
STATUS
approved