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 A188164 #5 Mar 30 2012 17:35:24 %S A188164 1,1,1,2,2,5,5,15,15,52,52,203,203,877,877,4140,4140,21147,21147, %T A188164 115975,115975,678570,678570,4213597,4213597,27644437,27644437, %U A188164 190899322,190899322,1382958545,1382958545 %N A188164 Number of palindromic structures of length n. %C A188164 Permuting the symbols does not change the structure; so e.g. aba and bab are equivalent. %F A188164 a(2n) = a(2n-1) = B(n), where B(n) = A000110(n) are the Bell numbers. %e A188164 For n=4, the 2 structures are aaaa and abba. For n=5, the 5 structures are aaaaa, aabaa, ababa, abbba, and abcba. %Y A188164 Cf. A000110, A056470, A056471, A164904. %K A188164 nonn %O A188164 0,4 %A A188164 _Franklin T. Adams-Watters_, Mar 23 2011