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 A180762 #11 Aug 21 2025 04:15:11 %S A180762 1,3,11,34,111,361,1172,3809,12377,40218,130687,424661,1379916, %T A180762 4483973,14570461,47346034,153848731,499924281,1624480652,5278674169, %U A180762 17152805697,55737242698,181115572487,588526611821,1912389796556,6214221516093 %N A180762 Half the number of nX2 binary arrays with each element equal to at least one neighbor. %C A180762 Column 2 of A180771 %H A180762 R. H. Hardin, <a href="/A180762/b180762.txt">Table of n, a(n) for n=1..99</a> %F A180762 Empirical: a(n) = 3*a(n-1) + a(n-2) - 2*a(n-4). %F A180762 Empirical g.f.: x*(1-x)*(1+x+2*x^2)/(1-3*x-x^2+2*x^4). - _Colin Barker_, Feb 22 2012 %K A180762 nonn %O A180762 1,2 %A A180762 _R. H. Hardin_ Sep 20 2010