a(n) = floor(n*(n-1)*(n-2)/12).

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =2a(5) =5a(6) =10a(7) =17a(8) =28a(9) =42a(10) =60a(11) =82a(12) =110a(13) =143a(14) =182a(15) =227a(16) =280a(17) =340a(18) =408a(19) =484a(20) =570a(21) =665a(22) =770a(23) =885a(24) =1012a(25) =1150a(26) =1300a(27) =1462a(28) =1638a(29) =1827