Number of ways to place 7 nonattacking queens on a 7 X n board.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =0a(7) =40a(8) =312a(9) =2038a(10) =9632a(11) =37248a(12) =120104a(13) =335010a(14) =835056a(15) =1897702a(16) =3998456a(17) =7907094a(18) =14818300a(19) =26512942a(20) =45562852a(21) =75580634a(22) =121520020a(23) =190031678a(24) =289879092a(25) =432420154a(26) =632159540a(27) =907376502a(28) =1280833348