256*n^8 - 448*n^6 + 240*n^4 - 40*n^2 + 1.

Terms

a(0) =1a(1) =9a(2) =40545a(3) =1372105a(4) =15003009a(5) =93149001a(6) =409389409a(7) =1423656585a(8) =4178507265a(9) =10783446409a(10) =25154396001a(11) =54085723209a(12) =108742564225a(13) =206671502025a(14) =374437978209a(15) =651009141001