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 A085569 #4 Mar 30 2012 16:49:45 %S A085569 1,1,3,1,15,3,7,15,45,5,231,21,455,315,45,3,1683,3465,7315,5005,3003, %T A085569 143,13455,585,6825,13923,3213,6545,515185,17765,110143,31977,2078505, %U A085569 62985,1789515,51129,210197,426075,246675,6325,1400355,34155,41612175,84192075 %N A085569 Denominator of 2*Sum(C(n,w)/(2*w+1),w=0..n/2-1)+C(n,n/2)/(n+1) if n is even, or of 2*Sum(C(n,w)/(2*w+1),w=0..(n-1)/2) if n is odd. %e A085569 1, 2, 8/3, 4, 88/15, 28/3, 104/7, 376/15, 1904/45, 372/5, 30152/231, ... %p A085569 b := binomial; f1 := n->if n mod 2 = 0 then 2*add(b(n,w)/(2*w+1),w=0..n/2-1)+b(n,n/2)/(n+1); else 2*add(b(n,w)/(2*w+1),w=0..(n-1)/2); fi; %Y A085569 Cf. A085568-A086673. %K A085569 nonn,frac %O A085569 0,3 %A A085569 _N. J. A. Sloane_, Jul 07 2003