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 A302509 #6 Sep 16 2020 18:56:44 %S A302509 1,3,11,28,90,458,4558,82857,1748514,44378638,1537387012,96444437992, %T A302509 9693542232011,1237134041433890,196120841811367262, %U A302509 47516901892945494991,19045444458145286230306 %N A302509 Number of n X n 0..1 arrays with every element equal to 0, 1, 4 or 5 horizontally, diagonally or antidiagonally adjacent elements, with upper left element zero. %C A302509 Diagonal of A302515. %e A302509 Some solutions for n=5 %e A302509 ..0..1..0..1..0. .0..1..0..1..0. .0..1..1..1..0. .0..1..0..1..1 %e A302509 ..0..0..1..1..0. .0..0..0..1..0. .0..1..0..1..0. .0..1..0..0..0 %e A302509 ..0..1..0..1..0. .0..1..1..1..0. .0..1..0..1..0. .0..1..1..1..0 %e A302509 ..0..1..0..1..0. .0..1..0..0..0. .0..0..0..1..0. .0..0..0..1..0 %e A302509 ..0..1..1..1..0. .0..1..0..1..0. .1..1..0..1..0. .0..1..0..1..0 %Y A302509 Cf. A302515. %K A302509 nonn %O A302509 1,2 %A A302509 _R. H. Hardin_, Apr 09 2018