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

Terms

a(0) =1a(1) =1a(2) =2a(3) =3a(4) =5a(5) =9a(6) =15a(7) =26a(8) =46a(9) =79a(10) =138a(11) =241a(12) =418a(13) =729a(14) =1270a(15) =2209a(16) =3849a(17) =6703a(18) =11669a(19) =20325a(20) =35393a(21) =61629a(22) =107329a(23) =186900a(24) =325464a(25) =566779a(26) =986987a(27) =1718745a(28) =2993062a(29) =5212135