a(n) = n*(6*n^2 - 7*n + 3)/2.

Terms

a(0) =0a(1) =1a(2) =13a(3) =54a(4) =142a(5) =295a(6) =531a(7) =868a(8) =1324a(9) =1917a(10) =2665a(11) =3586a(12) =4698a(13) =6019a(14) =7567a(15) =9360a(16) =11416a(17) =13753a(18) =16389a(19) =19342a(20) =22630a(21) =26271a(22) =30283a(23) =34684a(24) =39492a(25) =44725a(26) =50401a(27) =56538a(28) =63154a(29) =70267