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 A294849 #18 Jul 26 2018 07:05:39 %S A294849 0,1,2,3,5,6,9,10,13,15,18,19,23,24,27,31,36,37,42,43,48,52,55,56,62, %T A294849 65,68,72,79,80 %N A294849 a(n) is the total number of horizontal line segments that belong to the Dyck paths in the diagram of the symmetries of sigma described in A236104 and A237593 after n-th stage, with a(0) = 0. %C A294849 Since the diagram is symmetrics a(n) is also the number of vertical line segments after n-th stage. For a diagram see A293750. %F A294849 a(n) = A293750(n)/2. %Y A294849 Cf. A000203, A196020, A235791, A236104, A237048, A237591, A237593, A245092, A293750, A294847, A294848. %K A294849 nonn,more %O A294849 0,3 %A A294849 _Omar E. Pol_, Nov 09 2017