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

Terms

a(0) =1a(1) =0a(2) =0a(3) =0a(4) =1a(5) =4a(6) =10a(7) =20a(8) =39a(9) =88a(10) =228a(11) =600a(12) =1507a(13) =3652a(14) =8866a(15) =22100a(16) =56365a(17) =144656a(18) =369784a(19) =942480a(20) =2408934a(21) =6196280a(22) =16026652a(23) =41571640a(24) =107959654a(25) =280708560a(26) =731349400a(27) =1910098320a(28) =4999759830a(29) =13109582376