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 A223981 #8 Jul 23 2025 04:45:19 %S A223981 4,100,5029,358118,31831914,3322756326,392525216516,51162688962195, %T A223981 7224066705841458,1089938030989276020,173886286002145386302, %U A223981 29095306392044768817550,5072863442986308208335738 %N A223981 Number of n X n 0..3 arrays with rows unimodal and columns nondecreasing. %C A223981 Diagonal of A223987 %H A223981 R. H. Hardin, <a href="/A223981/b223981.txt">Table of n, a(n) for n = 1..14</a> %e A223981 Some solutions for n=3 %e A223981 ..0..2..1....0..2..0....0..1..2....0..3..1....1..1..2....0..2..0....1..3..0 %e A223981 ..2..2..1....1..3..0....0..1..2....1..3..3....1..1..2....0..2..1....2..3..0 %e A223981 ..2..2..2....1..3..3....2..2..3....1..3..3....3..2..2....0..3..3....2..3..2 %K A223981 nonn %O A223981 1,1 %A A223981 _R. H. Hardin_ Mar 30 2013