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 A193774 #6 Mar 31 2012 10:30:53 %S A193774 1,2,4,6,20,26,124,146,956,1050,9100 %N A193774 Number of signed permutations of length n invariant under the reverse complement and avoiding (-2, 1) and (2, -1). %e A193774 For n = 2, the permutations are (1, 2), (2, 1), (-1, -2), and (-2, -1). %K A193774 nonn %O A193774 0,2 %A A193774 _Andy Hardt_, Aug 04 2011