OFFSET
0,2
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..198
FORMULA
a(n) ~ 4^n * exp((2/LambertW(2) - 3)*n) * n^(2*n) / (sqrt(1 + LambertW(2)) * LambertW(2)^(2*n)).
MAPLE
b:= proc(n, k) option remember; `if`(n=0, 1,
(1+add(binomial(n-1, j-1)*b(n-j, k), j=1..n-1))*k)
end:
a:= n-> b(2*n, n):
seq(a(n), n=0..14); # Alois P. Heinz, Jul 27 2021
MATHEMATICA
Table[BellB[2*n, n], {n, 0, 20}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Vaclav Kotesovec, Jul 27 2021
STATUS
approved