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

Terms

a(0) =0a(1) =1a(2) =6a(3) =13a(4) =26a(5) =47a(6) =82a(7) =139a(8) =232a(9) =383a(10) =628a(11) =1025a(12) =1668a(13) =2709a(14) =4394a(15) =7121a(16) =11534a(17) =18675a(18) =30230a(19) =48927a(20) =79180a(21) =128131a(22) =207336a(23) =335493a(24) =542856a(25) =878377a(26) =1421262a(27) =2299669a(28) =3720962a(29) =6020663