OFFSET
0,4
FORMULA
a(0) = 1; a(n) = 2 * Sum_{k=3..n} binomial(n-1,k-1) * (k-1)! * a(n-k).
a(n) = Sum_{k=0..n} binomial(n,k) * Hermite(k,-1) * (n-k+1)!.
a(n) ~ exp(-3) * n * n!. - Vaclav Kotesovec, Aug 09 2021
D-finite with recurrence a(n) +(-n+1)*a(n-1) -2*(n-1)*(n-2)*a(n-3)=0. - R. J. Mathar, Aug 20 2021
MAPLE
A335595 := proc(n)
option remember ;
if n = 0 then
1;
else
2*add(binomial(n-1, k-1)*(k-1)!*procname(n-k), k=3..n) ;
end if;
end proc:
seq(A335595(n), n=0..42) ; # R. J. Mathar, Aug 20 2021
MATHEMATICA
nmax = 23; CoefficientList[Series[Exp[-x (2 + x)]/(1 - x)^2, {x, 0, nmax}], x] Range[0, nmax]!
a[0] = 1; a[n_] := a[n] = 2 Sum[Binomial[n - 1, k - 1] (k - 1)! a[n - k], {k, 3, n}]; Table[a[n], {n, 0, 23}]
Table[Sum[Binomial[n, k] HermiteH[k, -1] (n - k + 1)!, {k, 0, n}], {n, 0, 23}]
PROG
(PARI) my(x='x+O('x^30)); Vec(serlaplace(exp(-x*(2+x))/(1-x)^2)) \\ Michel Marcus, Nov 21 2020
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Nov 20 2020
STATUS
approved