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 A213804 #8 Apr 08 2020 01:56:26 %S A213804 1,1760,526443,34725760,932587453,13937940952,138198204339, %T A213804 1012226679296,5875958390949,28376054552968,118033137259563, %U A213804 433946033473016,1438074947544977,4362051703339832,12258717265789491,32233542519648928,79941392042719253,188248433874383736,423266982431567911 %N A213804 Number of 6 X 6 0..n symmetric arrays with all rows summing to 3*n. %e A213804 Some solutions for n=4 %e A213804 ..2..4..0..4..0..2....2..4..3..3..0..0....2..1..3..0..2..4....2..0..2..3..1..4 %e A213804 ..4..1..2..4..0..1....4..3..3..1..0..1....1..2..4..3..0..2....0..4..3..3..1..1 %e A213804 ..0..2..3..0..4..3....3..3..3..2..0..1....3..4..1..2..0..2....2..3..3..0..3..1 %e A213804 ..4..4..0..2..0..2....3..1..2..0..4..2....0..3..2..3..3..1....3..3..0..0..3..3 %e A213804 ..0..0..4..0..4..4....0..0..0..4..4..4....2..0..0..3..4..3....1..1..3..3..2..2 %e A213804 ..2..1..3..2..4..0....0..1..1..2..4..4....4..2..2..1..3..0....4..1..1..3..2..1 %Y A213804 Row 6 of A213800. %K A213804 nonn %O A213804 0,2 %A A213804 _R. H. Hardin_, Jun 20 2012 %E A213804 a(0)=1 prepended and terms a(12) and beyond from _Andrew Howroyd_, Apr 07 2020