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 A213792 #9 Apr 08 2020 17:14:11 %S A213792 1,1,3,29,3249,4843626,138198204339,87098380004205128, %T A213792 1525223999399549983474977 %N A213792 Number of n X n 0..n symmetric arrays with every row summing to floor(n^2/2). %e A213792 Some solutions for n=4 %e A213792 ..4..4..0..0....3..2..1..2....4..2..0..2....1..3..1..3....2..1..3..2 %e A213792 ..4..4..0..0....2..1..2..3....2..0..4..2....3..4..0..1....1..4..0..3 %e A213792 ..0..0..4..4....1..2..3..2....0..4..1..3....1..0..3..4....3..0..2..3 %e A213792 ..0..0..4..4....2..3..2..1....2..2..3..1....3..1..4..0....2..3..3..0 %Y A213792 Diagonal of A213800. %K A213792 nonn,more %O A213792 0,3 %A A213792 _R. H. Hardin_, Jun 20 2012 %E A213792 a(0)=1 prepended and a(7)-a(8) from _Andrew Howroyd_, Apr 07 2020