OFFSET
0,2
FORMULA
E.g.f.: exp(2*Sum_{k>=1} x^(k^2)).
a(0) = 1; a(n) = Sum_{k=1..n} A000122(k)*k!*binomial(n-1,k-1)*a(n-k).
MAPLE
seq(coeff(series(factorial(n)*(exp(2*add(x^(k^2), k=1..n))), x, n+1), x, n), n = 0 .. 25); # Muniru A Asiru, Oct 23 2018
MATHEMATICA
nmax = 22; CoefficientList[Series[Exp[EllipticTheta[3, 0, x] - 1], {x, 0, nmax}], x] Range[0, nmax]!
a[n_] := a[n] = Sum[SquaresR[1, k] k! Binomial[n - 1, k - 1] a[n - k], {k, 1, n}]; a[0] = 1; Table[a[n], {n, 0, 22}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Oct 23 2018
STATUS
approved