a(n) = n * (binomial(n,2) - 2).

Terms

a(0) =0a(1) =-2a(2) =-2a(3) =3a(4) =16a(5) =40a(6) =78a(7) =133a(8) =208a(9) =306a(10) =430a(11) =583a(12) =768a(13) =988a(14) =1246a(15) =1545a(16) =1888a(17) =2278a(18) =2718a(19) =3211a(20) =3760a(21) =4368a(22) =5038a(23) =5773a(24) =6576a(25) =7450a(26) =8398a(27) =9423a(28) =10528a(29) =11716