a(n) = n*(n + 1)*(17*n - 14)/6.

Terms

a(0) =0a(1) =1a(2) =20a(3) =74a(4) =180a(5) =355a(6) =616a(7) =980a(8) =1464a(9) =2085a(10) =2860a(11) =3806a(12) =4940a(13) =6279a(14) =7840a(15) =9640a(16) =11696a(17) =14025a(18) =16644a(19) =19570a(20) =22820a(21) =26411a(22) =30360a(23) =34684a(24) =39400a(25) =44525a(26) =50076a(27) =56070a(28) =62524a(29) =69455