a(n) = floor(n*(n+1)*(n+2) / (n + n+1 + n+2)) = floor(n*(n+2)/3).

Terms

a(0) =0a(1) =1a(2) =2a(3) =5a(4) =8a(5) =11a(6) =16a(7) =21a(8) =26a(9) =33a(10) =40a(11) =47a(12) =56a(13) =65a(14) =74a(15) =85a(16) =96a(17) =107a(18) =120a(19) =133a(20) =146a(21) =161a(22) =176a(23) =191a(24) =208a(25) =225a(26) =242a(27) =261a(28) =280a(29) =299