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 A261204 #32 Sep 19 2015 03:26:42 %S A261204 1,2,4,6,10,16,24,34,50,72,100,138,188,254,342,454,598,784,1018,1316, %T A261204 1694,2166,2756,3492,4404,5530,6920,8626,10712,13264,16368,20134, %U A261204 24700,30212,36856,44850,54438,65918,79642,96008,115488,138642,166100,198614,237062 %N A261204 Number of binary strings of length n that avoid the pattern x x^R x (x^R is the reversal of x). %H A261204 Giovanni Resta, <a href="/A261204/b261204.txt">Table of n, a(n) for n = 0..100</a> %H A261204 James D. Currie, Narad Rampersad, <a href="http://arxiv.org/abs/1508.02964">Binary words avoiding x x^R x and strongly unimodal sequences</a>, arXiv:1508.02964 [math.CO], 2015. %H A261204 James D. Currie, Narad Rampersad, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL18/Currie/currie12.html">Binary words avoiding x x^R x and strongly unimodal sequences</a>, Journal of Integer Sequences, Vol. 18 (2015), Article 15.10.3. %e A261204 For n = 6, the substrings to be avoided are 000, 111, 011001, and 100110. There are 26 binary strings that avoid 000 and 111, so there are 26 - 2 = 24 binary strings of length 6 that avoid x x^R x. %Y A261204 Cf. A028445, A241903. %K A261204 nonn %O A261204 0,2 %A A261204 _Narad Rampersad_, Aug 11 2015 %E A261204 a(25)-a(44) from _Giovanni Resta_, Aug 12 2015