G.f. satisfies A(x) = 1/(1 - 5*x) - x*A(x)^3.

Terms

a(0) =1a(1) =4a(2) =13a(3) =38a(4) =135a(5) =677a(6) =3538a(7) =15868a(8) =63313a(9) =268430a(10) =1348190a(11) =7038185a(12) =33328258a(13) =144159428a(14) =642323050a(15) =3213846836a(16) =16700677289a(17) =80935833050a(18) =363843867265