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 A298049 #6 May 03 2020 15:42:12 %S A298049 0,3,15,40,121,512,1708,7014,35804,201703,1158266,7391098,54852360 %N A298049 Number of n X n 0..1 arrays with every element equal to 1, 2, 4 or 6 king-move adjacent elements, with upper left element zero. %C A298049 Diagonal of A298055. %e A298049 Some solutions for n=5 %e A298049 ..0..0..1..0..0. .0..0..0..1..0. .0..0..0..1..0. .0..1..1..1..0 %e A298049 ..1..1..0..1..1. .1..1..1..0..1. .1..1..1..0..0. .1..0..0..0..1 %e A298049 ..0..1..1..1..0. .0..1..1..0..0. .0..0..0..0..0. .0..0..1..0..0 %e A298049 ..0..1..0..1..0. .0..1..1..1..1. .0..1..0..1..0. .1..1..0..1..1 %e A298049 ..1..0..1..0..1. .1..1..1..0..0. .1..1..0..1..1. .1..0..1..0..1 %Y A298049 Cf. A298055. %K A298049 nonn %O A298049 1,2 %A A298049 _R. H. Hardin_, Jan 11 2018