G.f.: Sum_{n>=1} (2*(1+x)^n - 1) * ((1+x)^n - 1)^(n-1).
A220266
G.f.: Sum_{n>=1} (2*(1+x)^n - 1) * ((1+x)^n - 1)^(n-1).
Terms
- a(0) =1a(1) =4a(2) =18a(3) =144a(4) =1604a(5) =22944a(6) =400624a(7) =8259680a(8) =196358760a(9) =5287879092a(10) =159094582274
External references
- oeis: A220266