a(n) = floor(n*(n-1)*(n-2)/24).

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =1a(5) =2a(6) =5a(7) =8a(8) =14a(9) =21a(10) =30a(11) =41a(12) =55a(13) =71a(14) =91a(15) =113a(16) =140a(17) =170a(18) =204a(19) =242a(20) =285a(21) =332a(22) =385a(23) =442a(24) =506a(25) =575a(26) =650a(27) =731a(28) =819a(29) =913