a(n) = (4n+1)^7.

Terms

a(0) =1a(1) =78125a(2) =4782969a(3) =62748517a(4) =410338673a(5) =1801088541a(6) =6103515625a(7) =17249876309a(8) =42618442977a(9) =94931877133a(10) =194754273881a(11) =373669453125a(12) =678223072849