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 A278771 #6 Apr 21 2020 12:54:28 %S A278771 0,2,266,19750,1673658,251740932,90752836672,93037538287080, %T A278771 293564184229043556,2953569640505846392444 %N A278771 Number of n X n 0..1 arrays with rows in nondecreasing lexicographic order and columns in nonincreasing lexicographic order, but with exactly two mistakes. %C A278771 Diagonal of A278778. %e A278771 Some solutions for n=4 %e A278771 ..1..0..0..0. .0..0..0..0. .1..0..0..1. .1..1..0..0. .0..0..1..0 %e A278771 ..1..1..0..1. .1..0..1..0. .1..1..1..1. .0..0..1..1. .1..0..0..0 %e A278771 ..1..1..0..1. .0..0..0..0. .0..0..0..0. .0..0..1..0. .0..0..0..0 %e A278771 ..1..0..0..0. .0..0..0..1. .1..1..1..0. .1..0..1..0. .0..0..1..1 %Y A278771 Cf. A278778. %K A278771 nonn %O A278771 1,2 %A A278771 _R. H. Hardin_, Nov 28 2016