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 A227406 #20 Sep 22 2013 20:40:32
%S A227406 1,2,16,372,24616,5014592,3349471840,7649590386464,61356625102897216,
%T A227406 1758844330913892684288,182379122144778004351027200,
%U A227406 69026760045145802122822210022400,96048744530120196897251255933762037760,494360393380904255996973467025921794482614272
%N A227406 Number of unimodal functions f:[n]->[2^n].
%H A227406 Alois P. Heinz, <a href="/A227406/b227406.txt">Table of n, a(n) for n = 0..50</a>
%F A227406 a(n) = Sum_{j=0..2^n-1} C(n+2*j-1,2*j).
%F A227406 a(n) = A071921(n,2^n).
%F A227406 a(n) ~ 2^(n^2+n-1)/n!. - _Vaclav Kotesovec_, Sep 22 2013
%p A227406 a:= n-> sum(binomial(n+2*j-1, 2*j), j=0..2^n-1):
%p A227406 seq(a(n), n=0..20);
%t A227406 Table[Sum[Binomial[n+2*j-1,2*j],{j,0,2^n-1}],{n,0,15}] (* _Vaclav Kotesovec_, Sep 22 2013 *)
%Y A227406 Cf. A071920, A227402.
%K A227406 nonn
%O A227406 0,2
%A A227406 _Alois P. Heinz_, Sep 21 2013