O.g.f.: Sum_{n>=0} n!^2 * x^n * Product_{k=1..n} (1 + x) / (1 + k^2*x + k^2*x^2).
A221371
O.g.f.: Sum_{n>=0} n!^2 * x^n * Product_{k=1..n} (1 + x) / (1 + k^2*x + k^2*x^2).
Terms
- a(0) =1a(1) =1a(2) =4a(3) =23a(4) =209a(5) =2744a(6) =49539a(7) =1180281a(8) =35921892a(9) =1360513711a(10) =62770245601
External references
- oeis: A221371