G.f. = b(2)^2*b(4)/(x^5+x^4-x^3-x^2-x+1), where b(k) = (1-x^k)/(1-x).

Terms

a(0) =1a(1) =4a(2) =9a(3) =18a(4) =33a(5) =56a(6) =94a(7) =156a(8) =255a(9) =416a(10) =677a(11) =1098a(12) =1780a(13) =2884a(14) =4669a(15) =7558a(16) =12233a(17) =19796a(18) =32034a(19) =51836a(20) =83875a(21) =135716a(22) =219597a(23) =355318a(24) =574920a(25) =930244a(26) =1505169a(27) =2435418a(28) =3940593a(29) =6376016