If n mod 2 = 0 then n*(n^2-4)/12 else n*(n^2-1)/12.

Terms

a(0) =0a(1) =0a(2) =0a(3) =2a(4) =4a(5) =10a(6) =16a(7) =28a(8) =40a(9) =60a(10) =80a(11) =110a(12) =140a(13) =182a(14) =224a(15) =280a(16) =336a(17) =408a(18) =480a(19) =570a(20) =660a(21) =770a(22) =880a(23) =1012a(24) =1144a(25) =1300a(26) =1456a(27) =1638a(28) =1820a(29) =2030