a(n) = floor(n*(n - 1)*(n - 2)/31).

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =1a(6) =3a(7) =6a(8) =10a(9) =16a(10) =23a(11) =31a(12) =42a(13) =55a(14) =70a(15) =88a(16) =108a(17) =131a(18) =157a(19) =187a(20) =220a(21) =257a(22) =298a(23) =342a(24) =391a(25) =445a(26) =503a(27) =566a(28) =634a(29) =707