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 A213793 #8 Apr 08 2020 17:13:46 %S A213793 1,1,2,4,18,112,1760,35150,1944530,133948836,26615510712, %T A213793 6549149852112,4762109992158288,4274712091685443584, %U A213793 11528251571501588791296,38295413179145036856212700,386860001875783390762182911250,4805622573099374975572752075805000 %N A213793 Number of n X n 0..1 symmetric arrays with every row summing to floor(n/2). %H A213793 Andrew Howroyd, <a href="/A213793/b213793.txt">Table of n, a(n) for n = 0..24</a> %F A213793 a(2*n) = A333164(n). - _Andrew Howroyd_, Apr 08 2020 %e A213793 Some solutions for n=4 %e A213793 ..1..1..0..0....0..0..1..1....0..1..1..0....1..0..1..0....0..1..1..0 %e A213793 ..1..0..1..0....0..0..1..1....1..0..0..1....0..0..1..1....1..1..0..0 %e A213793 ..0..1..0..1....1..1..0..0....1..0..0..1....1..1..0..0....1..0..0..1 %e A213793 ..0..0..1..1....1..1..0..0....0..1..1..0....0..1..0..1....0..0..1..1 %Y A213793 Column 1 of A213800. %Y A213793 Cf. A333164. %K A213793 nonn %O A213793 0,3 %A A213793 _R. H. Hardin_, Jun 20 2012 %E A213793 a(0)=1 prepended and terms a(13) and beyond from _Andrew Howroyd_, Apr 08 2020