This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A238838 #8 Mar 16 2014 18:13:22 %S A238838 2,48,5760,5806080,75246796800,1780537083494400,115939740156316876800, %T A238838 19864514173849162481664000 %N A238838 Number of 2n X 2n addition squares in which every digram (s,s;), s' != s, appears once horizontally and once vertically. %H A238838 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 A238838 a(n) = (2*n)!*A141599(n)^2/phi(n). %Y A238838 Cf. A000315, A002860, A000010, A141599. %K A238838 nonn,more %O A238838 1,1 %A A238838 _N. J. A. Sloane_, Mar 15 2014