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 A259423 #6 Jun 02 2025 11:51:11 %S A259423 469,7695,123306,1990133,32060569,516880938,8331704179,134312969201, %T A259423 2165188798924,34904319329031,562681121125617,9070816244710226, %U A259423 146227977764091271,2357299291195098509,38001348653396589778 %N A259423 Number of (n+1)X(4+1) 0..1 arrays with each 2X2 subblock having clockwise pattern 0000 0001 0011 or 0111. %C A259423 Column 4 of A259427 %H A259423 R. H. Hardin, <a href="/A259423/b259423.txt">Table of n, a(n) for n = 1..210</a> %F A259423 Empirical: a(n) = 18*a(n-1) +34*a(n-2) -1078*a(n-3) -384*a(n-4) +17595*a(n-5) -3702*a(n-6) -104436*a(n-7) +47348*a(n-8) +254812*a(n-9) -155015*a(n-10) -240597*a(n-11) +170095*a(n-12) +72147*a(n-13) -60513*a(n-14) -2266*a(n-15) +6147*a(n-16) -594*a(n-17) -142*a(n-18) +25*a(n-19) -a(n-20) %e A259423 Some solutions for n=3 %e A259423 ..0..0..1..1..0....0..1..1..1..1....0..0..1..1..0....1..0..1..0..0 %e A259423 ..1..0..0..0..0....0..1..0..1..0....1..1..1..0..0....1..1..1..0..1 %e A259423 ..0..0..0..0..0....0..1..0..1..0....0..0..1..0..0....0..0..1..0..0 %e A259423 ..0..0..0..0..0....0..0..0..1..1....1..0..0..0..0....0..1..1..1..1 %Y A259423 Cf. A259427 %K A259423 nonn %O A259423 1,1 %A A259423 _R. H. Hardin_, Jun 26 2015