a(n) = (n^9 - n)/10.

Terms

a(0) =0a(1) =51a(2) =1968a(3) =26214a(4) =195312a(5) =1007769a(6) =4035360a(7) =13421772a(8) =38742048a(9) =99999999a(10) =235794768a(11) =515978034a(12) =1060449936a(13) =2066104677a(14) =3844335936a(15) =6871947672a(16) =11858787648a(17) =19835929035a(18) =32268769776a(19) =51199999998a(20) =79428004656a(21) =120726921777a(22) =180115266144a(23) =264180754020