a(n) = floor( n*(n-1)*(n-2)/5 ).

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =4a(5) =12a(6) =24a(7) =42a(8) =67a(9) =100a(10) =144a(11) =198a(12) =264a(13) =343a(14) =436a(15) =546a(16) =672a(17) =816a(18) =979a(19) =1162a(20) =1368a(21) =1596a(22) =1848a(23) =2125a(24) =2428a(25) =2760a(26) =3120a(27) =3510a(28) =3931a(29) =4384