G.f.: Sum_{n>=0} Product_{k=1..n} ((1+x)^(3*k-1) - 1).

A207571

G.f.: Sum_{n>=0} Product_{k=1..n} ((1+x)^(3*k-1) - 1).

Terms

    a(0) =1a(1) =2a(2) =11a(3) =105a(4) =1390a(5) =23520a(6) =484247a(7) =11742927a(8) =327711230a(9) =10343198878a(10) =364237027076

External references