G.f.: A(x) = 1 + x*(1 + x*(1 + x*(...(1 + x*(...)^(3n))...)^9)^6)^3.
A138213
G.f.: A(x) = 1 + x*(1 + x*(1 + x*(...(1 + x*(...)^(3n))...)^9)^6)^3.
Terms
- a(0) =1a(1) =1a(2) =3a(3) =21a(4) =244a(5) =4002a(6) =84909a(7) =2209947a(8) =68121822a(9) =2425846806a(10) =97969327890
External references
- oeis: A138213