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 A220331 #5 Sep 03 2022 20:56:15 %S A220331 1,37,508,6657,92093,1335202,18836493,265346645,3750121527 %N A220331 Equals two maps: number of 4 X n binary arrays indicating the locations of corresponding elements equal to exactly two of their horizontal and antidiagonal neighbors in a random 0..1 4 X n array. %C A220331 Row 4 of A220328. %e A220331 Some solutions for n=3 %e A220331 ..0..0..1....0..1..0....0..0..0....0..0..1....0..0..1....0..1..0....0..0..1 %e A220331 ..1..0..1....0..1..0....0..1..1....1..0..0....1..1..0....0..1..0....0..0..0 %e A220331 ..0..0..1....1..0..0....0..0..0....0..1..0....0..0..1....1..1..1....0..0..0 %e A220331 ..1..0..0....0..0..0....0..1..0....0..1..0....0..0..0....0..1..0....1..1..0 %Y A220331 Cf. A220328. %K A220331 nonn %O A220331 1,2 %A A220331 _R. H. Hardin_, Dec 10 2012