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 A300640 #6 Aug 20 2020 11:37:28 %S A300640 0,1,2,64,2998,456649,209156119,280782187131,1114340919987573, %T A300640 12994612967873847001,446094799302794492462850 %N A300640 Number of n X n 0..1 arrays with every element equal to 2, 3, 4 or 5 horizontally, vertically or antidiagonally adjacent elements, with upper left element zero. %C A300640 Diagonal of A300646. %e A300640 Some solutions for n=5 %e A300640 ..0..0..0..0..1. .0..0..1..1..0. .0..0..0..0..0. .0..0..1..1..0 %e A300640 ..0..1..0..1..1. .0..0..1..0..0. .0..0..1..0..1. .0..1..1..0..0 %e A300640 ..1..1..0..1..1. .0..1..1..1..1. .0..1..1..1..1. .0..0..0..1..1 %e A300640 ..1..1..0..1..0. .0..0..1..1..0. .0..1..0..0..0. .1..1..0..1..1 %e A300640 ..1..0..0..0..0. .0..0..1..0..0. .0..0..0..0..0. .1..0..0..1..1 %Y A300640 Cf. A300646. %K A300640 nonn %O A300640 1,3 %A A300640 _R. H. Hardin_, Mar 10 2018