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 A213700 #6 Jul 22 2025 23:03:34 %S A213700 529,750261,109820000,4286833981,83545858925,976919547736, %T A213700 8159542628448,51964311225934,271341777491743,1197645088919101, %U A213700 4637119560078960,16013821321719463,50395763900241707,145985579644461562 %N A213700 Half the number of 5X5 0..n symmetric arrays with no 2X2 subblock summing to 2n. %C A213700 Row 4 of A213697 %H A213700 R. H. Hardin, <a href="/A213700/b213700.txt">Table of n, a(n) for n = 1..33</a> %e A213700 Some solutions for n=4 %e A213700 ..0..3..2..3..4....3..0..0..1..4....0..4..0..2..3....0..1..2..2..4 %e A213700 ..3..4..3..1..3....0..2..3..1..1....4..2..0..3..3....1..2..4..1..0 %e A213700 ..2..3..4..2..4....0..3..2..4..3....0..0..4..3..1....2..4..2..3..1 %e A213700 ..3..1..2..4..1....1..1..4..1..4....2..3..3..2..0....2..1..3..1..4 %e A213700 ..4..3..4..1..1....4..1..3..4..3....3..3..1..0..4....4..0..1..4..4 %K A213700 nonn %O A213700 1,1 %A A213700 _R. H. Hardin_ Jun 18 2012