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 A181213 #6 Jul 22 2025 08:35:58 %S A181213 2,16,400,28561,7133488,5037592576,11494250657760,81903288018125025, %T A181213 1774095560440527819780,120560883729040740095954944, %U A181213 25387802734116842287569948104640,16523941893729018365186706701633818689 %N A181213 Number of n X n binary matrices with no three 1's adjacent in a line diagonally or antidiagonally. %C A181213 Diagonal of A181217 %H A181213 R. H. Hardin, <a href="/A181213/b181213.txt">Table of n, a(n) for n=1..20</a> %e A181213 Some avoided solutions for 4X4 %e A181213 ..1..0..0..0....0..0..0..0....0..0..0..1....0..1..0..0....0..0..1..0 %e A181213 ..0..1..0..0....0..0..1..1....0..1..1..0....0..0..1..0....0..1..0..0 %e A181213 ..0..0..1..1....0..0..1..0....0..1..0..0....1..0..0..1....1..0..0..0 %e A181213 ..0..0..0..0....0..1..0..0....0..0..0..0....0..0..0..0....0..0..1..0 %K A181213 nonn %O A181213 1,1 %A A181213 _R. H. Hardin_ Oct 10 2010