[ n(n-1)(n-2)(n-3)/17 ].

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =1a(5) =7a(6) =21a(7) =49a(8) =98a(9) =177a(10) =296a(11) =465a(12) =698a(13) =1009a(14) =1413a(15) =1927a(16) =2569a(17) =3360a(18) =4320a(19) =5472a(20) =6840a(21) =8449a(22) =10327a(23) =12501a(24) =15001a(25) =17858a(26) =21105a(27) =24776a(28) =28905a(29) =33530