a(n) = n*(8*n^2 - 5)/3.

Terms

a(0) =0a(1) =1a(2) =18a(3) =67a(4) =164a(5) =325a(6) =566a(7) =903a(8) =1352a(9) =1929a(10) =2650a(11) =3531a(12) =4588a(13) =5837a(14) =7294a(15) =8975a(16) =10896a(17) =13073a(18) =15522a(19) =18259a(20) =21300a(21) =24661a(22) =28358a(23) =32407a(24) =36824a(25) =41625a(26) =46826a(27) =52443a(28) =58492a(29) =64989