a(n) = (7n)^5.

Terms

a(0) =0a(1) =16807a(2) =537824a(3) =4084101a(4) =17210368a(5) =52521875a(6) =130691232a(7) =282475249a(8) =550731776a(9) =992436543a(10) =1680700000a(11) =2706784157a(12) =4182119424a(13) =6240321451a(14) =9039207968a(15) =12762815625a(16) =17623416832a(17) =23863536599a(18) =31757969376a(19) =41615795893a(20) =53782400000a(21) =68641485507a(22) =86617093024