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 A198434 #11 Mar 31 2012 10:32:05 %S A198434 2,10,90,966,12338,181470,3018082,55995486,1146939010,25716746430, %T A198434 626755197698,16502357651966,466944932413442,14133259249586174, %U A198434 455715081098876418,15596665064842012158,564724372634695925762,21568978799171323200510,866674159679235417061378,36548294282449538711357438 %N A198434 Number of simple symmetric permutations of degree 2n (or 2n+1). %C A198434 A permutation is simple if the only intervals that are fixed are the singletons and [1..m]. %C A198434 A permutation p is symmetric if i+j=m+1 implies p(i)+p(j)=m+1. %C A198434 For example the permutations %C A198434 1234 and 12345 %C A198434 2413 25314 %C A198434 are both simple and symmetric. %C A198434 Symmetric simple permutations of degree 2n+1 correspond to simple permutations in the Weyl group of type B_n. %C A198434 Symmetric simple permutations of degree 2n correspond to simple permutations in the Weyl group of type C_n. %C A198434 These occur in pairs so all entries in this sequence will be even. %H A198434 R. Dewji, I. Dimitrov, A. McCabe, M. Roth, D. Wehlau and J. Wilson, %H A198434 <a href="http://arxiv.org/abs/1110.5880">Decomposing Inversion Sets of Permutations and Applications to Faces of the Littlewood-Richardson Cone</a>, arXiv:1110.5880v1[math.CO] %e A198434 The simple symmetric permutations of lowest degree are 2413, 3142, 25314, 41325. %Y A198434 Cf. A111111. %K A198434 nonn %O A198434 2,1 %A A198434 _David Wehlau_, Oct 24 2011