Number of ways to arrange 3 nonattacking knights on the lower triangle of an n X n board.

Terms

a(0) =0a(1) =1a(2) =12a(3) =62a(4) =253a(5) =804a(6) =2136a(7) =4958a(8) =10376a(9) =20013a(10) =36144a(11) =61846a(12) =101163a(13) =159286a(14) =242748a(15) =359634a(16) =519806a(17) =735143a(18) =1019796a(19) =1390458a(20) =1866649a(21) =2471016a(22) =3229648a(23) =4172406a(24) =5333268a(25) =6750689a(26) =8467976a(27) =10533678a(28) =13001991a(29) =15933178