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 A177475 #10 Oct 02 2024 10:53:01 %S A177475 1,1,2,6,20,81,390,2161,13678,96983,764368,6630898,62748250,643442919, %T A177475 7104914398,84062375725,1060919238874,14226075039395,201982580807466, %U A177475 3027049675655253,47753241018325280,790998083929598213,13726222157931958274,249018700470309832015,4714071198944211367704 %N A177475 Number of permutations of order n avoiding the consecutive pattern 131'2. %C A177475 To avoid 131'2 means not to have four consecutive letters such that if the third letter is removed, then in the obtained 3 letter word the smallest letter is the first one, and the largest letter is the second one. %H A177475 S. Kitaev, <a href="https://doi.org/10.1016/j.dam.2006.09.011">Introduction to partially ordered patterns</a>, Discrete Applied Mathematics 155 (2007), 929-944. %H A177475 S. Kitaev, <a href="https://personal.strath.ac.uk/sergey.kitaev/Papers/intro-to-pops.pdf">Introduction to partially ordered patterns</a>. %Y A177475 Cf. A117156, A177470, A177471, A177472, A177473, A177476, A177477, A177478, A177479, A177480, A177481, A177482, A177483, A177484, A376694. %K A177475 nonn %O A177475 0,3 %A A177475 Signy Olafsdottir (signy06(AT)ru.is), May 09 2010 %E A177475 Edited and terms a(0),a(10)-a(24) added by _Max Alekseyev_, Oct 02 2024