Number of non-equivalent ways to place 4 non-attacking ferses on an n X n board.

Terms

a(0) =0a(1) =0a(2) =6a(3) =92a(4) =832a(5) =4500a(6) =18229a(7) =58881a(8) =163509a(9) =401259a(10) =898420a(11) =1861146a(12) =3625546a(13) =6694982a(14) =11829267a(15) =20099815a(16) =33036079a(17) =52700901a(18) =81916834a(19) =124362664a(20) =184907220a(21) =269726216a(22) =386776561a(23) =545930397a(24) =759628777a(25) =1043027055a(26) =1414873104a(27) =1897655046a(28) =2518755934a(29) =3310591194