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 A301945 #7 Apr 20 2020 00:03:11 %S A301945 0,2,20,947,120815,58609226,86143630040,418568449327270, %T A301945 6527100767589040926,331808147283786972146018, %U A301945 54543586667142977292165721500,29084806316831133817614992597097070 %N A301945 Number of n X n 0..1 arrays with every element equal to 1, 2 or 3 horizontally or antidiagonally adjacent elements, with upper left element zero. %C A301945 Diagonal of A301951. %H A301945 R. H. Hardin, <a href="/A301945/b301945.txt">Table of n, a(n) for n = 1..13</a> %e A301945 Some solutions for n=5 %e A301945 ..0..0..0..0..0. .0..0..0..1..1. .0..0..1..1..0. .0..0..0..1..1 %e A301945 ..0..1..0..1..1. .0..1..0..0..0. .0..1..1..0..0. .0..1..0..0..0 %e A301945 ..1..1..1..0..0. .1..0..1..1..0. .1..0..1..0..0. .1..1..1..0..0 %e A301945 ..1..0..0..0..1. .0..0..1..0..1. .0..1..1..1..1. .1..0..0..1..0 %e A301945 ..1..1..1..1..1. .0..1..0..1..1. .1..0..0..0..0. .0..1..1..0..0 %Y A301945 Cf. A301951. %K A301945 nonn %O A301945 1,2 %A A301945 _R. H. Hardin_, Mar 29 2018