OFFSET
0,3
FORMULA
a(n) = n*A247499(n - 1) for n >= 1.
a(n) = Sum_{k=1..n} binomial(n, k)^2 * k! / (n - k + 1), for n >= 1.
MAPLE
MATHEMATICA
a[0] = 1; a[n_] := Sum[Binomial[n, k]^2 * k!/(n - k + 1), {k, 1, n}]; Array[a, 20, 0] (* Amiram Eldar, Jan 09 2022 *)
PROG
(PARI) a(n) = if (n == 0, 1, sum(k=1, n, binomial(n, k)^2 * k! / (n - k + 1))); \\ Michel Marcus, Jan 09 2022 [a(0) corrected by Georg Fischer, Jun 22 2022]
CROSSREFS
KEYWORD
nonn
AUTHOR
Peter Luschny, Jan 09 2022
STATUS
approved