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

Terms

a(0) =1a(1) =5a(2) =9a(3) =17a(4) =29a(5) =49a(6) =81a(7) =133a(8) =217a(9) =353a(10) =573a(11) =929a(12) =1505a(13) =2437a(14) =3945a(15) =6385a(16) =10333a(17) =16721a(18) =27057a(19) =43781a(20) =70841a(21) =114625a(22) =185469a(23) =300097a(24) =485569a(25) =785669a(26) =1271241a(27) =2056913a(28) =3328157a(29) =5385073