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 A301993 #6 Aug 20 2020 11:48:31 %S A301993 0,2,5,74,2856,100176,15243860,3267873712,1423142192108, %T A301993 1493258497764034,2656316754272813006,10809582885066864547012, %U A301993 85481211759186744525328998,1368540960166632565900365694716 %N A301993 Number of n X n 0..1 arrays with every element equal to 1, 2 or 4 horizontally or antidiagonally adjacent elements, with upper left element zero. %C A301993 Diagonal of A301999. %e A301993 Some solutions for n=5 %e A301993 ..0..0..1..1..0. .0..0..1..1..0. .0..0..1..1..0. .0..0..1..1..1 %e A301993 ..0..0..1..0..1. .0..1..0..0..1. .0..0..1..0..0. .0..1..0..1..0 %e A301993 ..0..0..1..1..1. .1..1..1..1..1. .1..1..1..0..0. .1..0..0..0..0 %e A301993 ..0..1..1..0..1. .0..0..1..1..1. .1..1..1..1..1. .1..1..0..1..0 %e A301993 ..0..0..0..1..1. .0..0..1..0..0. .1..0..0..0..0. .1..0..1..0..0 %Y A301993 Cf. A301999. %K A301993 nonn %O A301993 1,2 %A A301993 _R. H. Hardin_, Mar 30 2018