a(n) = floor(C(n,4)/5).

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =1a(6) =3a(7) =7a(8) =14a(9) =25a(10) =42a(11) =66a(12) =99a(13) =143a(14) =200a(15) =273a(16) =364a(17) =476a(18) =612a(19) =775a(20) =969a(21) =1197a(22) =1463a(23) =1771a(24) =2125a(25) =2530a(26) =2990a(27) =3510a(28) =4095a(29) =4750