G.f. = b(2)*b(6)/(x^6-x^4+x^2-2*x+1), where b(k) = (1-x^k)/(1-x).

Terms

a(0) =1a(1) =4a(2) =9a(3) =16a(4) =26a(5) =42a(6) =67a(7) =104a(8) =158a(9) =238a(10) =359a(11) =542a(12) =816a(13) =1224a(14) =1833a(15) =2746a(16) =4116a(17) =6168a(18) =9237a(19) =13828a(20) =20702a(21) =30998a(22) =46415a(23) =69492a(24) =104034a(25) =155746a(26) =233171a(27) =349090a(28) =522628a(29) =782420