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 A301609 #6 Aug 20 2020 11:46:26 %S A301609 0,3,62,3816,758338,488491106,1019565752074,6897694015722898, %T A301609 151249886315100454600,10749578188598491367494716 %N A301609 Number of n X n 0..1 arrays with every element equal to 1, 2 or 3 horizontally or vertically adjacent elements, with upper left element zero. %C A301609 Diagonal of A301615. %e A301609 Some solutions for n=5 %e A301609 ..0..0..0..0..0. .0..0..0..0..0. .0..0..0..0..0. .0..0..0..0..0 %e A301609 ..0..0..0..1..1. .0..0..1..0..1. .1..1..1..1..1. .1..1..1..1..1 %e A301609 ..0..1..1..1..1. .1..1..1..0..1. .1..1..0..0..1. .0..0..1..0..0 %e A301609 ..0..0..0..0..1. .0..0..0..1..0. .1..0..0..1..1. .0..0..1..0..0 %e A301609 ..1..1..0..1..1. .1..1..0..1..0. .0..0..0..1..1. .0..0..1..0..0 %Y A301609 Cf. A301615. %K A301609 nonn %O A301609 1,2 %A A301609 _R. H. Hardin_, Mar 24 2018