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%I #8 Mar 16 2014 18:13:22
%S 2,48,5760,5806080,75246796800,1780537083494400,115939740156316876800,
%T 19864514173849162481664000
%N Number of 2n X 2n addition squares in which every digram (s,s;), s' != s, appears once horizontally and once vertically.
%H Gilbert, E. N., <a href="http://www.jstor.org/stable/2027267">Latin squares which contain no repeated digrams</a>, SIAM Rev. 7 1965 189--198. MR0179095 (31 #3346).
%F a(n) = (2*n)!*A141599(n)^2/phi(n).
%Y Cf. A000315, A002860, A000010, A141599.
%K nonn,more
%O 1,1
%A _N. J. A. Sloane_, Mar 15 2014