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 A208263 #9 Jul 22 2025 21:15:38 %S A208263 1,7,161,11929,2867739,2234126207,5641457245533,46171961042899417, %T A208263 1224814800337927770335,105309458529148583423889079, %U A208263 29347371781481633173790977728301,26507936613513086328494176843991041391 %N A208263 Number of n X n 0..1 arrays with new values 0..1 introduced in row major order and no element equal to more than two of its immediate leftward or upward or left-upward diagonal neighbors. %C A208263 Diagonal of A208269 %H A208263 R. H. Hardin, <a href="/A208263/b208263.txt">Table of n, a(n) for n = 1..19</a> %e A208263 Some solutions for n=4 %e A208263 ..0..0..1..0....0..1..0..1....0..0..0..1....0..0..0..1....0..0..1..0 %e A208263 ..0..1..1..0....0..0..1..0....0..1..1..0....1..0..1..1....1..0..0..0 %e A208263 ..1..1..0..0....1..1..1..0....1..1..0..1....0..0..1..0....0..1..1..0 %e A208263 ..1..0..0..1....0..1..0..0....0..0..1..0....0..1..0..0....1..0..1..0 %K A208263 nonn %O A208263 1,2 %A A208263 _R. H. Hardin_ Feb 24 2012