a(n) = 4*n*(21*n - 26).

Terms

a(0) =0a(1) =-20a(2) =128a(3) =444a(4) =928a(5) =1580a(6) =2400a(7) =3388a(8) =4544a(9) =5868a(10) =7360a(11) =9020a(12) =10848a(13) =12844a(14) =15008a(15) =17340a(16) =19840a(17) =22508a(18) =25344a(19) =28348a(20) =31520a(21) =34860a(22) =38368a(23) =42044a(24) =45888a(25) =49900a(26) =54080a(27) =58428a(28) =62944a(29) =67628