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

Terms

a(0) =3a(1) =7a(2) =15a(3) =37a(4) =93a(5) =239a(6) =619a(7) =1611a(8) =4203a(9) =10981a(10) =28713a(11) =75115a(12) =196563a(13) =514463a(14) =1346647a(15) =3525189a(16) =9228453a(17) =24159415a(18) =63248571a(19) =165584323a(20) =433501203a(21) =1134914117a(22) =2971232785a(23) =7778770707a(24) =20365057443a(25) =53316366199a(26) =139583983839a(27) =365435492581