a(n) = floor(n*(n-1)*(n-2)/30).

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =2a(6) =4a(7) =7a(8) =11a(9) =16a(10) =24a(11) =33a(12) =44a(13) =57a(14) =72a(15) =91a(16) =112a(17) =136a(18) =163a(19) =193a(20) =228a(21) =266a(22) =308a(23) =354a(24) =404a(25) =460a(26) =520a(27) =585a(28) =655a(29) =730