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 A242155 #9 Feb 10 2015 06:54:44
%S A242155 1,3,12,50,240,1281,7588,49392,350775,2700115,22399476,199258488,
%T A242155 1892343362,19111149225,204532683600,2312443695920,27541725738255,
%U A242155 344681838284220,4522200516582650,62068382381998440,889492878311173290,13286058811968721515
%N A242155 Number of ascent sequences of length n with exactly two flat steps.
%H A242155 Joerg Arndt and Alois P. Heinz, <a href="/A242155/b242155.txt">Table of n, a(n) for n = 3..140</a>
%F A242155 a(n) ~ Pi^(3/2)/(2*sqrt(3)*exp(Pi^2/12)) * (6/Pi^2)^n * n! * sqrt(n). - _Vaclav Kotesovec_, Aug 27 2014
%t A242155 b[n_, i_, t_] := b[n, i, t] = If[n == 0, 1, Expand[Sum[ If[j == i, x, 1]*b[n - 1, j, t + If[j > i, 1, 0]], {j, 0, t + 1}]]]; a[n_] := Coefficient[b[n, -1, -1], x, 2]; Table[a[n], {n, 3, 30}] (* _Jean-François Alcover_, Feb 10 2015, after A242153 *)
%Y A242155 Column k=2 of A242153.
%K A242155 nonn
%O A242155 3,2
%A A242155 _Joerg Arndt_ and _Alois P. Heinz_, May 05 2014