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 A242543 #8 Jul 23 2025 11:17:06 %S A242543 12,32,88,242,660,1800,4920,13448,36736,100352,274176,749088,2046528, %T A242543 5591168,15275392,41733248,114017280,311500800,851036160,2325074432, %U A242543 6352221184,17354590208,47413622784,129536428032,353900101632 %N A242543 Number of length n+3 0..2 arrays with no four elements in a row with pattern aabb (possibly a=b) and new values 0..2 introduced in 0..2 order. %C A242543 Column 2 of A242549 %H A242543 R. H. Hardin, <a href="/A242543/b242543.txt">Table of n, a(n) for n = 1..210</a> %F A242543 Empirical: a(n) = 2*a(n-1) +4*a(n-3) +4*a(n-4). %F A242543 Empirical: G.f.: -2*x*(6+4*x+12*x^2+9*x^3) / ( (2*x^2+2*x-1)*(2*x^2+1) ). - _R. J. Mathar_, May 18 2014 %e A242543 Some solutions for n=4 %e A242543 ..0....0....0....0....0....0....0....0....0....0....0....0....0....0....0....0 %e A242543 ..0....1....1....1....1....1....1....1....0....0....1....1....0....0....1....1 %e A242543 ..1....1....0....2....0....0....1....1....0....1....0....0....1....1....0....0 %e A242543 ..2....1....0....1....0....2....2....0....1....2....0....2....0....0....1....2 %e A242543 ..1....2....0....0....2....0....0....1....2....0....1....0....0....0....0....1 %e A242543 ..1....1....1....1....0....1....2....0....2....0....2....0....0....2....0....1 %e A242543 ..0....2....0....2....1....1....0....0....1....1....1....1....1....1....0....2 %K A242543 nonn %O A242543 1,1 %A A242543 _R. H. Hardin_, May 17 2014