a(n) = Sum_{k=0..n} C(n,k) * (2 + 3^k)^(n-k).

A244756

a(n) = Sum_{k=0..n} C(n,k) * (2 + 3^k)^(n-k).

Terms

    a(0) =1a(1) =4a(2) =20a(3) =136a(4) =1424a(5) =25504a(6) =831680a(7) =49526656a(8) =5359464704

External references