a(n) = floor(n*(n-1)*(n-2)/9).

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =2a(5) =6a(6) =13a(7) =23a(8) =37a(9) =56a(10) =80a(11) =110a(12) =146a(13) =190a(14) =242a(15) =303a(16) =373a(17) =453a(18) =544a(19) =646a(20) =760a(21) =886a(22) =1026a(23) =1180a(24) =1349a(25) =1533a(26) =1733a(27) =1950a(28) =2184a(29) =2436