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 A205187 #7 Jul 22 2025 18:36:54 %S A205187 16,24,48,72,144,216,432,648,1296,1944,3888,5832,11664,17496,34992, %T A205187 52488,104976,157464,314928,472392,944784,1417176,2834352,4251528, %U A205187 8503056,12754584,25509168,38263752,76527504,114791256,229582512,344373768 %N A205187 Number of (n+1)X2 0..1 arrays with the number of clockwise edge increases in every 2X2 subblock differing from each horizontal or vertical neighbor. %C A205187 Column 1 of A205193 %H A205187 R. H. Hardin, <a href="/A205187/b205187.txt">Table of n, a(n) for n = 1..210</a> %F A205187 Empirical: a(n) = 3*a(n-2) %e A205187 Some solutions for n=4 %e A205187 ..1..0....0..0....1..1....0..1....1..1....1..1....0..1....0..1....0..0....1..1 %e A205187 ..0..1....0..0....0..0....1..1....1..1....0..1....0..1....1..0....1..0....1..1 %e A205187 ..0..1....1..1....0..0....1..1....0..0....1..0....1..0....0..0....0..1....1..0 %e A205187 ..1..0....1..1....0..1....0..0....0..0....0..0....0..0....0..0....1..1....0..1 %e A205187 ..1..0....0..0....1..0....0..0....1..0....0..0....0..0....0..1....1..1....0..1 %K A205187 nonn %O A205187 1,1 %A A205187 _R. H. Hardin_ Jan 23 2012