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 A288539 #12 Jun 11 2017 15:57:29 %S A288539 1,0,1,2,8,25,83,282,971,3386,11940,42504,152546,551426,2005930, %T A288539 7337901,26976726,99618976,369349607,1374391706,5131186060, %U A288539 19214759396,72152791729,271629133830,1024989876797,3876208984221,14688301498888,55763768987236,212077310097784 %N A288539 Number of Dyck paths of semilength n such that at least one positive level has no peaks. %C A288539 a(0) = 1 by convention. %H A288539 Alois P. Heinz, <a href="/A288539/b288539.txt">Table of n, a(n) for n = 0..300</a> %H A288539 Wikipedia, <a href="https://en.wikipedia.org/wiki/Lattice_path#Counting_lattice_paths">Counting lattice paths</a> %e A288539 : a(3) = 2: %e A288539 : /\ %e A288539 : /\/\ / \ %e A288539 : / \ / \ . %Y A288539 Column k=0 of A288387. %Y A288539 Cf. A000108. %K A288539 nonn %O A288539 0,4 %A A288539 _Alois P. Heinz_, Jun 11 2017