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

Terms

a(0) =1a(1) =1a(2) =3a(3) =5a(4) =12a(5) =20a(6) =42a(7) =74a(8) =148a(9) =264a(10) =506a(11) =918a(12) =1730a(13) =3154a(14) =5876a(15) =10760a(16) =19938a(17) =36574a(18) =67536a(19) =124048a(20) =228664a(21) =420248a(22) =773878a(23) =1422790a(24) =2618646a(25) =4815314a(26) =8859904a(27) =16293864a(28) =29974958a(29) =55128726