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

Terms

a(0) =3a(1) =4a(2) =8a(3) =17a(4) =40a(5) =98a(6) =247a(7) =632a(8) =1632a(9) =4237a(10) =11036a(11) =28802a(12) =75259a(13) =196796a(14) =514840a(15) =1347257a(16) =3526176a(17) =9230050a(18) =24161999a(19) =63252752a(20) =165591088a(21) =433512149a(22) =1134931828a(23) =2971261442a(24) =7778817075a(25) =20365132468a(26) =53316487592a(27) =139584180257a(28) =365435810392