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) =4a(3) =10a(4) =27a(5) =70a(6) =184a(7) =481a(8) =1260a(9) =3298a(10) =8635a(11) =22606a(12) =59184a(13) =154945a(14) =405652a(15) =1062010a(16) =2780379a(17) =7279126a(18) =19057000a(19) =49891873a(20) =130618620a(21) =341963986a(22) =895273339a(23) =2343856030a(24) =6136294752a(25) =16065028225a(26) =42058789924a(27) =110111341546a(28) =288275234715a(29) =754714362598