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 A240650 #7 Jul 23 2025 11:05:08 %S A240650 1,2,9,91,2456,184819,37066859,18940533171,24272278810439, %T A240650 77660940030730106 %N A240650 Number of n X n 0..1 arrays with no element equal to exactly one horizontal or vertical neighbor, with new values 0..1 introduced in row major order. %C A240650 Diagonal of A240656 %e A240650 Some solutions for n=4 %e A240650 ..0..0..0..0....0..0..0..1....0..0..1..1....0..1..0..0....0..0..0..1 %e A240650 ..0..1..0..0....0..0..0..0....0..0..1..1....1..0..0..0....0..0..0..0 %e A240650 ..0..0..1..0....0..1..0..0....0..0..0..0....0..0..1..0....0..0..0..0 %e A240650 ..1..0..0..0....0..0..0..0....0..0..0..0....0..0..0..0....1..0..0..0 %K A240650 nonn %O A240650 1,2 %A A240650 _R. H. Hardin_, Apr 09 2014