a(n) = floor(n(n-1)/8).

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =1a(5) =2a(6) =3a(7) =5a(8) =7a(9) =9a(10) =11a(11) =13a(12) =16a(13) =19a(14) =22a(15) =26a(16) =30a(17) =34a(18) =38a(19) =42a(20) =47a(21) =52a(22) =57a(23) =63a(24) =69a(25) =75a(26) =81a(27) =87a(28) =94a(29) =101