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 A260835 #6 Jun 02 2025 12:11:28 %S A260835 82,131,288,496,796,1645,2976,4890,9332,17659,30090,54846,104380, %T A260835 184549,329454,618800,1121728,1998197,3692344,6772932,12142202, %U A260835 22172787,40769872,73664484,133728146,245325455,445857864,808254626,1477620470 %N A260835 Number of (n+2)X(2+2) 0..1 arrays with each 3X3 subblock having clockwise perimeter pattern 00000001 00000011 or 00010101. %C A260835 Column 2 of A260841 %H A260835 R. H. Hardin, <a href="/A260835/b260835.txt">Table of n, a(n) for n = 1..210</a> %F A260835 Empirical: a(n) = a(n-1) +5*a(n-3) -a(n-4) -3*a(n-5) -5*a(n-6) +3*a(n-9) -2*a(n-10) -5*a(n-11) -2*a(n-12) -a(n-13) +5*a(n-14) -2*a(n-15) -2*a(n-17) +2*a(n-18) for n>19 %e A260835 Some solutions for n=4 %e A260835 ..1..0..1..0....0..1..1..0....1..0..1..1....0..0..0..0....0..0..0..1 %e A260835 ..0..1..0..1....0..0..0..0....0..0..0..0....0..0..0..0....0..0..1..0 %e A260835 ..1..0..0..0....0..0..0..0....1..0..0..0....1..0..0..1....0..0..0..0 %e A260835 ..0..1..0..0....1..1..0..0....0..0..0..1....0..0..0..1....0..0..0..0 %e A260835 ..0..0..0..0....0..0..0..0....0..0..0..0....0..0..0..0....0..1..0..0 %e A260835 ..0..0..0..0....0..0..0..0....0..1..0..1....1..1..0..1....1..1..0..0 %Y A260835 Cf. A260841 %K A260835 nonn %O A260835 1,1 %A A260835 _R. H. Hardin_, Aug 01 2015