a(n) = n*(7*n^2-12*n+7)/2.

Terms

a(0) =0a(1) =1a(2) =11a(3) =51a(4) =142a(5) =305a(6) =561a(7) =931a(8) =1436a(9) =2097a(10) =2935a(11) =3971a(12) =5226a(13) =6721a(14) =8477a(15) =10515a(16) =12856a(17) =15521a(18) =18531a(19) =21907a(20) =25670a(21) =29841a(22) =34441a(23) =39491a(24) =45012a(25) =51025a(26) =57551a(27) =64611a(28) =72226a(29) =80417