a(n) = floor(n*(n-1)/24).

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =1a(7) =1a(8) =2a(9) =3a(10) =3a(11) =4a(12) =5a(13) =6a(14) =7a(15) =8a(16) =10a(17) =11a(18) =12a(19) =14a(20) =15a(21) =17a(22) =19a(23) =21a(24) =23a(25) =25a(26) =27a(27) =29a(28) =31a(29) =33