Number of ways to place 4 nonattacking queens on an n X n board.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =2a(5) =82a(6) =982a(7) =7002a(8) =34568a(9) =131248a(10) =412596a(11) =1123832a(12) =2739386a(13) =6106214a(14) =12654614a(15) =24675650a(16) =45704724a(17) =80999104a(18) =138170148a(19) =227938788a(20) =365106738a(21) =569681574a(22) =868289594a(23) =1295775946a(24) =1897176508a(25) =2729909796