a(n) = floor(n*(n-1)*(n-2)/15).

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =1a(5) =4a(6) =8a(7) =14a(8) =22a(9) =33a(10) =48a(11) =66a(12) =88a(13) =114a(14) =145a(15) =182a(16) =224a(17) =272a(18) =326a(19) =387a(20) =456a(21) =532a(22) =616a(23) =708a(24) =809a(25) =920a(26) =1040a(27) =1170a(28) =1310a(29) =1461