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 A192089 #7 Mar 31 2012 10:29:58 %S A192089 0,0,6,66,402,2028,8790,35118,131982,475344,1658382,5651226,18912498, %T A192089 62418180,203768862,659487678,2119617474,6774043254,21547968726, %U A192089 68274910026,215609878962,678936947940,2132568719358,6683705385078,20906259913566,65277851607840 %N A192089 Number of permutations of [n] that require a 3-letter alphabet in order to be realized by a shift. %C A192089 These permutations are those realized by the shift on 3 letters (A192088) %C A192089 but not by the shift on 2 letters (A059413). %D A192089 S. Elizalde, The number of permutations realized by a shift, SIAM J. Discrete Math. 23 (2009), 765--786. %H A192089 Sergi Elizalde, <a href="http://arxiv.org/abs/0909.2274">The number of permutations realized by a shift</a>, arXiv:0909.2274v1 [math.CO] %F A192089 a(n)=3^(n-2)+sum(psi_3(t)*3^(n-t-1),t=1..n-1)-n*sum(psi_2(t)*2^(n-t-1),t=0..n-1), where psi_N(t) is the number of primitive words of length t over an N-letter alphabet, which is expressible in terms of the Möbius function. %e A192089 a(4)=6 because the permutations 1423, 3241, 4132, 2314 3421, 2134 are the only ones of length 4 that require 3 letters in order to be realized by a shift %Y A192089 Equals A192088 minus A059413 %K A192089 nonn %O A192089 2,3 %A A192089 _Sergi Elizalde_, Jun 23 2011