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) =7a(3) =19a(4) =42a(5) =82a(6) =150a(7) =263a(8) =449a(9) =753a(10) =1248a(11) =2052a(12) =3356a(13) =5469a(14) =8891a(15) =14431a(16) =23398a(17) =37910a(18) =61394a(19) =99395a(20) =160885a(21) =260381a(22) =421372a(23) =681864a(24) =1103352a(25) =1785337a(26) =2888815a(27) =4674283a(28) =7563234a(29) =12237658