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 A175386 #8 Oct 15 2013 10:12:31
%S A175386 1,2,6,4,5,4,7,8,18,10,11,24,13,14,30,16,17,12,19,20,42,22,23,48,25,
%T A175386 26,54,28,29,20,31,32,66,34,35,72,37,38,78,40,41,28,43,44,90,46,47,96,
%U A175386 49,50,6,52,53,36,55,56,114,58,59,120,61,62,126,64,65,44,67,68,138,70,71
%N A175386 a(n) = denominator of sum((1/i)*C(2n-i-1,i-1),i=1..n).
%C A175386 We conjecture that sum((1/i)*C(2n-i-1,i-1),i=1..n) is not an integer for n>1.
%F A175386 According to Mathematica, sum((1/i)*C(2n-i-1,i-1), i=1..n)=
%F A175386 (Hypergeometric2F1[1/2-n,-n,1-2 n,-4]-1)/(2 n).
%t A175386 Table[Denominator[Sum[(1/i)*Binomial[2n-i-1,i-1],{i,1,n}]],{n,1,150}]
%Y A175386 Cf. A175385.
%K A175386 frac,nonn
%O A175386 1,2
%A A175386 _Zak Seidov_, _Vladimir Shevelev_, Apr 24 2010