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

Terms

a(0) =1a(1) =2a(2) =4a(3) =9a(4) =20a(5) =46a(6) =105a(7) =243a(8) =560a(9) =1296a(10) =2994a(11) =6928a(12) =16019a(13) =37060a(14) =85713a(15) =198282a(16) =458636a(17) =1060932a(18) =2454070a(19) =5676750a(20) =13131210a(21) =30374892a(22) =70262196a(23) =162528916a(24) =375957183a(25) =869654746a(26) =2011661506a(27) =4653323265a(28) =10763942479a(29) =24898869052