Constant term of the reduction by x^2->x+1 of the polynomial p(n,x) = 1 + x^n + x^(2n).

Terms

a(0) =2a(1) =4a(2) =7a(3) =16a(4) =38a(5) =95a(6) =242a(7) =624a(8) =1619a(9) =4216a(10) =11002a(11) =28747a(12) =75170a(13) =196652a(14) =514607a(15) =1346880a(16) =3525566a(17) =9229063a(18) =24160402a(19) =63250168a(20) =165586907a(21) =433505384a(22) =1134920882a(23) =2971243731a(24) =7778788418a(25) =20365086100a(26) =53316412567a(27) =139584058864a(28) =365435613974a(29) =956722540271