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 A100561 #5 Dec 24 2014 20:06:50
%S A100561 1,1,2,3,12,10,60,105,140,63,280,1155,27720,25740,8008,9009,16380,
%T A100561 17017,6126120,2909907,5542680,2645370,232792560,111546435,535422888,
%U A100561 128707425,2974571600,717084225,80313433200,77636318760,2329089562800,4512611027925,546983154900
%N A100561 Denominator of Sum_{k=0..[n/2]} 1/binomial(n,k).
%e A100561 1, 3/2, 4/3, 17/12, 13/10, 77/60, 128/105, 167/140, 73/63, 319/280, 1294/1155, 30697/27720, 28211/25740, 8707/8008, 9728/9009, 17587/16380, 18181/17017, ... = A100560/A100561
%t A100561 Denominator[Table[Sum[1/Binomial[n,k],{k,0,Floor[n/2]}],{n,0,40}]] (* _Harvey P. Dale_, Dec 24 2014 *)
%K A100561 nonn,frac
%O A100561 0,3
%A A100561 _N. J. A. Sloane_, Nov 28 2004