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 A281049 #6 Apr 21 2020 13:00:19 %S A281049 0,1,68,1022,7803,46610,221212,926077,3549039,12749511,43675963, %T A281049 144504080,466130380 %N A281049 Number of n X n 0..1 arrays with no element equal to more than one of its horizontal and antidiagonal neighbors, with the exception of exactly two elements, and with new values introduced in order 0 sequentially upwards. %C A281049 Diagonal of A281056. %e A281049 Some solutions for n=4 %e A281049 ..0..1..0..0. .0..1..1..0. .0..1..1..0. .0..1..1..0. .0..1..0..1 %e A281049 ..0..1..1..0. .0..0..1..0. .0..0..1..1. .0..1..1..0. .0..1..0..1 %e A281049 ..0..0..0..0. .0..1..1..0. .1..0..1..0. .1..0..1..1. .1..0..1..0 %e A281049 ..1..0..1..1. .1..0..1..0. .0..0..1..1. .1..0..0..1. .1..1..1..0 %Y A281049 Cf. A281056. %K A281049 nonn %O A281049 1,3 %A A281049 _R. H. Hardin_, Jan 13 2017