G.f. A(x) satisfies: A(x) = 1 + x + x^2 + x^3 * A(x/(1 - x)) / (1 - x)^2.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =3a(5) =7a(6) =15a(7) =33a(8) =81a(9) =225a(10) =679a(11) =2139a(12) =6931a(13) =23185a(14) =80809a(15) =295141a(16) =1128487a(17) =4492363a(18) =18506923a(19) =78584193a(20) =343414489a(21) =1544535129a(22) =7151822771a(23) =34086446307a(24) =167058478355a(25) =840700482197