a(n) = [x^n] (1 + x*(1+x)^(n+1) )^(n+1).
A121680
a(n) = [x^n] (1 + x*(1+x)^(n+1) )^(n+1).
Terms
- a(0) =1a(1) =2a(2) =12a(3) =76a(4) =655a(5) =6816a(6) =81690a(7) =1109816a(8) =16782399a(9) =278438740a(10) =5016899833a(11) =97368894756
External references
- oeis: A121680