a(n) = (1/n) * Sum_{k=0..n-1} binomial(n+k-1,k) * binomial(3*n,n-k-1) * (n-3)^k.
A366203
a(n) = (1/n) * Sum_{k=0..n-1} binomial(n+k-1,k) * binomial(3*n,n-k-1) * (n-3)^k.
Terms
- a(0) =1a(1) =2a(2) =12a(3) =156a(4) =3507a(5) =115692a(6) =5066364a(7) =276943568a(8) =18152243967
External references
- oeis: A366203