a(n):=(Sum_{k=0}^n C(6k,3k)C(3k,k)C(6(n-k),3(n-k))C(3(n-k),n-k))/((2n-1)Binomial[3n,n]).
A189286
a(n):=(Sum_{k=0}^n C(6k,3k)C(3k,k)C(6(n-k),3(n-k))C(3(n-k),n-k))/((2n-1)Binomial[3n,n]).
Terms
- a(0) =-1a(1) =40a(2) =696a(3) =23408a(4) =969496a(5) =44602560a(6) =2187147600a(7) =111957721920
External references
- oeis: A189286