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 A213955 #7 Jun 24 2023 18:14:57 %S A213955 2,10,138,5314,575122,176041978,153143689594,380082566144530, %T A213955 2699632942815871042,55016905649245690586122, %U A213955 3223966155402204759824471786 %N A213955 Number of n X n 0..1 matrices with row and column i=1..n having sum <= i. %e A213955 Some solutions for n=4 %e A213955 ..0..1..0..0....1..0..0..0....1..0..0..0....1..0..0..0....1..0..0..0 %e A213955 ..0..0..1..1....0..1..1..0....0..1..0..0....0..1..0..0....0..0..0..0 %e A213955 ..1..0..0..1....0..1..0..1....0..0..1..1....0..1..1..0....0..1..1..1 %e A213955 ..0..1..1..1....0..0..1..0....0..1..0..0....0..0..1..1....0..0..1..1 %Y A213955 Column 1 of A213962. %K A213955 nonn %O A213955 1,1 %A A213955 _R. H. Hardin_, Jun 28 2012