a(n) = floor(n*(n-1)*(n-2)/17).

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =1a(5) =3a(6) =7a(7) =12a(8) =19a(9) =29a(10) =42a(11) =58a(12) =77a(13) =100a(14) =128a(15) =160a(16) =197a(17) =240a(18) =288a(19) =342a(20) =402a(21) =469a(22) =543a(23) =625a(24) =714a(25) =811a(26) =917a(27) =1032a(28) =1156a(29) =1289