a(n) = (1/2) * Sum_{k=1..n} (n+k)! / k!.
A384929
a(n) = (1/2) * Sum_{k=1..n} (n+k)! / k!.
Terms
- a(0) =1a(1) =9a(2) =102a(3) =1500a(4) =27660a(5) =617400a(6) =16213680a(7) =490069440a(8) =16760882880a(9) =639966096000
External references
- oeis: A384929