a(n) = (2*n + 1)^7.

Terms

a(0) =1a(1) =2187a(2) =78125a(3) =823543a(4) =4782969a(5) =19487171a(6) =62748517a(7) =170859375a(8) =410338673a(9) =893871739a(10) =1801088541a(11) =3404825447a(12) =6103515625a(13) =10460353203a(14) =17249876309a(15) =27512614111a(16) =42618442977a(17) =64339296875a(18) =94931877133a(19) =137231006679a(20) =194754273881a(21) =271818611107a(22) =373669453125a(23) =506623120463