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

Terms

a(0) =0a(1) =1a(2) =2a(3) =7a(4) =18a(5) =49a(6) =128a(7) =337a(8) =882a(9) =2311a(10) =6050a(11) =15841a(12) =41472a(13) =108577a(14) =284258a(15) =744199a(16) =1948338a(17) =5100817a(18) =13354112a(19) =34961521a(20) =91530450a(21) =239629831a(22) =627359042a(23) =1642447297a(24) =4299982848a(25) =11257501249a(26) =29472520898a(27) =77160061447a(28) =202007663442a(29) =528862928881