G.f. satisfies A(x) = 1 + x*A(x)/(1 - x^4*A(x)^3).

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =2a(6) =6a(7) =16a(8) =36a(9) =72a(10) =139a(11) =283a(12) =631a(13) =1487a(14) =3510a(15) =8086a(16) =18240a(17) =41004a(18) =93364a(19) =216370a(20) =507353a(21) =1193113a(22) =2799681a(23) =6556243a(24) =15368798a(25) =36163695a(26) =85483537a(27) =202768647a(28) =481870474a(29) =1146143965