a(n) = binomial(n,floor(n/2))*(n+1)!.

A002867

a(n) = binomial(n,floor(n/2))*(n+1)!.

Terms

    a(0) =1a(1) =2a(2) =12a(3) =72a(4) =720a(5) =7200a(6) =100800a(7) =1411200a(8) =25401600a(9) =457228800a(10) =10059033600a(11) =221298739200

External references