a(n) = floor(n*(n-1)/14).

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =1a(6) =2a(7) =3a(8) =4a(9) =5a(10) =6a(11) =7a(12) =9a(13) =11a(14) =13a(15) =15a(16) =17a(17) =19a(18) =21a(19) =24a(20) =27a(21) =30a(22) =33a(23) =36a(24) =39a(25) =42a(26) =46a(27) =50a(28) =54a(29) =58