a(n) = floor(n*(n - 1)/11).

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =1a(5) =1a(6) =2a(7) =3a(8) =5a(9) =6a(10) =8a(11) =10a(12) =12a(13) =14a(14) =16a(15) =19a(16) =21a(17) =24a(18) =27a(19) =31a(20) =34a(21) =38a(22) =42a(23) =46a(24) =50a(25) =54a(26) =59a(27) =63a(28) =68a(29) =73