a(n) = (8*n + 1)^5.

Terms

a(0) =1a(1) =59049a(2) =1419857a(3) =9765625a(4) =39135393a(5) =115856201a(6) =282475249a(7) =601692057a(8) =1160290625a(9) =2073071593a(10) =3486784401a(11) =5584059449a(12) =8587340257a(13) =12762815625a(14) =18424351793a(15) =25937424601a(16) =35723051649a(17) =48261724457