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%I #7 Oct 05 2021 00:28:48
%S 1,4,2,1,1,5,2,15
%N Consider problem of placing A051755(n) queens on an n X n board so that each queen attacks precisely 2 others. Sequence gives number of solutions up to square symmetry.
%Y Cf. A051754-A051759, A051567-A051571, A019654.
%K nonn,nice,more
%O 2,2
%A Robert Trent (trentrd(AT)hotmail.com), Aug 23 2000
%E a(9) from _Sean A. Irvine_, Oct 05 2021