a(n) = Sum_{k=0..n} binomial(n,k) * (1 + 3^k)^k.

A244004

a(n) = Sum_{k=0..n} binomial(n,k) * (1 + 3^k)^k.

Terms

    a(0) =1a(1) =5a(2) =109a(3) =22265a(4) =45300601a(5) =865092893645

External references