Number of ways to arrange 5 nonattacking queens on the lower triangle of an n X n board.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =4a(7) =114a(8) =1384a(9) =9890a(10) =50662a(11) =205512a(12) =698688a(13) =2074530a(14) =5525902a(15) =13476246a(16) =30522678a(17) =64968996a(18) =131070600a(19) =252492296a(20) =467017054a(21) =833501728a(22) =1440839952a(23) =2420878990a(24) =3964168632a(25) =6342428908a(26) =9934738024a(27) =15264432954