G.f.: Sum_{n>=0} n! * (2*x)^n * Product_{k=1..n} (1 + k*x)/(1 + 2*k*x + 2*k^2*x^2).
A221988
G.f.: Sum_{n>=0} n! * (2*x)^n * Product_{k=1..n} (1 + k*x)/(1 + 2*k*x + 2*k^2*x^2).
Terms
- a(0) =1a(1) =2a(2) =6a(3) =24a(4) =116a(5) =664a(6) =4392a(7) =32928a(8) =276016a(9) =2557856a(10) =25965408a(11) =286538112a(12) =3415359296a(13) =43727878528a(14) =598510015104
External references
- oeis: A221988