OFFSET
0,3
FORMULA
E.g.f.: Series_Reversion( (1 - x)^2 * (1 - exp(-x)) ).
a(n) = Sum_{k=1..n} (2*n+k-2)!/(2*n-1)! * |Stirling1(n,k)|.
a(n) ~ LambertW(2*exp(3))^n * n^(n-1) / (sqrt(2*(1 + LambertW(2*exp(3)))) * (LambertW(2*exp(3)) - 2)^(3*n-1) * exp(n)). - Vaclav Kotesovec, Sep 10 2024
MATHEMATICA
Table[Sum[(2*n+k-2)!/(2*n-1)! * Abs[StirlingS1[n, k]], {k, 1, n}], {n, 0, 20}] (* Vaclav Kotesovec, Sep 10 2024 *)
PROG
(PARI) my(N=20, x='x+O('x^N)); concat(0, Vec(serlaplace(serreverse((1-x)^2*(1-exp(-x))))))
(PARI) a(n) = sum(k=1, n, (2*n+k-2)!/(2*n-1)!*abs(stirling(n, k, 1)));
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Mar 20 2024
STATUS
approved