a(n) = (n+2) * (2n+1) * (2n-1)! / (n-1)!.
A002691
a(n) = (n+2) * (2n+1) * (2n-1)! / (n-1)!.
Terms
- a(0) =1a(1) =9a(2) =120a(3) =2100a(4) =45360a(5) =1164240a(6) =34594560a(7) =1167566400a(8) =44108064000
External references
- oeis: A002691
A002691
a(n) = (n+2) * (2n+1) * (2n-1)! / (n-1)!.