G.f. = b(2)*b(6)/(3*x^6-2*x^5-2*x+1), where b(k) = (1-x^k)/(1-x).

Terms

a(0) =1a(1) =4a(2) =10a(3) =22a(4) =46a(5) =96a(6) =198a(7) =404a(8) =822a(9) =1670a(10) =3394a(11) =6896a(12) =14006a(13) =28444a(14) =57762a(15) =117302a(16) =238214a(17) =483752a(18) =982374a(19) =1994940a(20) =4051198a(21) =8226918a(22) =16706698a(23) =33926888a(24) =68896534a(25) =139910644a(26) =284121530a(27) =576975702a(28) =1171685086a(29) =2379382576