a(n) = floor(n^2/12).

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =1a(5) =2a(6) =3a(7) =4a(8) =5a(9) =6a(10) =8a(11) =10a(12) =12a(13) =14a(14) =16a(15) =18a(16) =21a(17) =24a(18) =27a(19) =30a(20) =33a(21) =36a(22) =40a(23) =44a(24) =48a(25) =52a(26) =56a(27) =60a(28) =65a(29) =70