G.f.: Sum_{n>=0} n^n * x^n * (1 + n*x)^n / (1 + n*x + n^2*x^2)^(n+1).
A240921
G.f.: Sum_{n>=0} n^n * x^n * (1 + n*x)^n / (1 + n*x + n^2*x^2)^(n+1).
Terms
- a(0) =1a(1) =1a(2) =3a(3) =18a(4) =146a(5) =1530a(6) =19620a(7) =297360a(8) =5201784a(9) =103146120a(10) =2286181800a(11) =56011087440
External references
- oeis: A240921