a(n) = Sum_{i=0..n} C(n,i)^2*i!*4^i + 2^n*n!.
A121079
a(n) = Sum_{i=0..n} C(n,i)^2*i!*4^i + 2^n*n!.
Terms
- a(0) =2a(1) =7a(2) =57a(3) =757a(4) =13889a(5) =322021a(6) =8962225a(7) =289928549a(8) =10666353409a(9) =439225736005
External references
- oeis: A121079