G.f. = b(2)*b(4)*b(6)/(x^9+x^8+x^7+x^6-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) =10a(3) =22a(4) =45a(5) =90a(6) =177a(7) =344a(8) =666a(9) =1286a(10) =2482a(11) =4788a(12) =9232a(13) =17798a(14) =34309a(15) =66136a(16) =127485a(17) =245738a(18) =473678a(19) =913046a(20) =1759956a(21) =3392428a(22) =6539118a(23) =12604558a(24) =24296069a(25) =46832182a(26) =90271937a(27) =174004756a(28) =335404954a(29) =646513838