a(n) = ((n^6 - (n-1)^6) - (n^2 - (n-1)^2))/60.

Terms

a(0) =0a(1) =1a(2) =11a(3) =56a(4) =192a(5) =517a(6) =1183a(7) =2408a(8) =4488a(9) =7809a(10) =12859a(11) =20240a(12) =30680a(13) =45045a(14) =64351a(15) =89776a(16) =122672a(17) =164577a(18) =217227a(19) =282568a(20) =362768a(21) =460229a(22) =577599a(23) =717784a(24) =883960a(25) =1079585a(26) =1308411a(27) =1574496a(28) =1882216a(29) =2236277