Seventh power of odd primes.

Terms

a(0) =2187a(1) =78125a(2) =823543a(3) =19487171a(4) =62748517a(5) =410338673a(6) =893871739a(7) =3404825447a(8) =17249876309a(9) =27512614111a(10) =94931877133a(11) =194754273881a(12) =271818611107a(13) =506623120463