Constant term in the reduction of the polynomial x^(2*n) + x^n + 1 by x^3 -> x + 1. See Comments.

Terms

a(0) =3a(1) =1a(2) =1a(3) =3a(4) =3a(5) =5a(6) =7a(7) =11a(8) =19a(9) =31a(10) =53a(11) =91a(12) =157a(13) =273a(14) =475a(15) =829a(16) =1449a(17) =2535a(18) =4439a(19) =7777a(20) =13631a(21) =23899a(22) =41911a(23) =73511a(24) =128953a(25) =226231a(26) =396921a(27) =696433a(28) =1222003a(29) =2144265