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 A208703 #9 Jul 22 2025 21:28:59 %S A208703 1,8,196,16084,4226368,3613193828,10001404535216,89755737081698964, %T A208703 2610569024927748701352,246105734855228896970291844, %U A208703 75198808251676193628977268566832,74474161314983311603786393034039933768 %N A208703 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 right-upward antidiagonal neighbors. %C A208703 Diagonal of A208709 %H A208703 R. H. Hardin, <a href="/A208703/b208703.txt">Table of n, a(n) for n = 1..20</a> %e A208703 Some solutions for n=4 %e A208703 ..0..0..1..0....0..0..0..1....0..1..0..1....0..0..0..1....0..1..1..0 %e A208703 ..0..0..1..0....1..0..1..1....1..0..1..1....1..0..0..0....0..0..1..0 %e A208703 ..1..1..0..0....0..0..1..0....0..0..0..1....1..1..1..1....0..0..1..1 %e A208703 ..1..1..0..0....0..1..0..0....0..1..0..1....1..0..1..1....1..0..0..0 %K A208703 nonn %O A208703 1,2 %A A208703 _R. H. Hardin_ Mar 01 2012