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

Terms

a(0) =1a(1) =2a(2) =5a(3) =13a(4) =35a(5) =94a(6) =252a(7) =678a(8) =1823a(9) =4900a(10) =13176a(11) =35427a(12) =95250a(13) =256105a(14) =688599a(15) =1851450a(16) =4978062a(17) =13384681a(18) =35987808a(19) =96761612a(20) =260166110a(21) =699517054a(22) =1880814358a(23) =5057006914a(24) =13596939262a(25) =36558534049a(26) =98296122593a(27) =264291989596a(28) =710610490247