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 A304264 #7 Apr 20 2020 00:07:57 %S A304264 1,1,6,21,146,1246,13767,252509,5755625,177353720,8354131403, %T A304264 523250794396,44173651472383,5428616779817049,920678621074132173, %U A304264 212277158481925445968,69198443091508695982216 %N A304264 Number of n X n 0..1 arrays with every element unequal to 0, 1, 5 or 8 king-move adjacent elements, with upper left element zero. %C A304264 Diagonal of A304270. %H A304264 R. H. Hardin, <a href="/A304264/b304264.txt">Table of n, a(n) for n = 1..22</a> %e A304264 Some solutions for n=5 %e A304264 ..0..0..1..0..0. .0..0..0..1..0. .0..0..0..0..0. .0..0..0..0..0 %e A304264 ..0..0..0..0..0. .0..0..0..0..0. .0..0..0..0..0. .0..0..0..0..1 %e A304264 ..0..0..0..0..0. .0..0..0..0..0. .1..0..0..0..0. .0..0..0..0..0 %e A304264 ..0..0..0..1..0. .0..0..0..0..1. .0..0..0..0..1. .1..0..0..0..0 %e A304264 ..0..0..0..0..0. .0..1..0..0..0. .0..0..0..0..0. .0..0..0..1..0 %Y A304264 Cf. A304270. %K A304264 nonn %O A304264 1,3 %A A304264 _R. H. Hardin_, May 09 2018