a(n) = Sum_{k=0..n} n^k * binomial(n+1,k) * binomial(n+1,k+1).

A331794

a(n) = Sum_{k=0..n} n^k * binomial(n+1,k) * binomial(n+1,k+1).

Terms

    a(0) =1a(1) =4a(2) =33a(3) =400a(4) =6285a(5) =120456a(6) =2714173a(7) =70129984a(8) =2040655401a(9) =65956468600

External references