a(n) = n! * Sum_{k=0..n} k^(2*k)/k!.

A356691

a(n) = n! * Sum_{k=0..n} k^(2*k)/k!.

Terms

    a(0) =1a(1) =2a(2) =20a(3) =789a(4) =68692a(5) =10109085a(6) =2237436846a(7) =693885130771

External references