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 A191999 #11 Mar 30 2012 18:49:34 %S A191999 1,2,8,16,160,640,2048,12288,24576,32768,327680,786432,10485760, %T A191999 62914560,125829120,167772160,9730785280,583847116800,3503082700800, %U A191999 245215789056000 %N A191999 Denominators of partial products of a Hardy-Littlewood constant. %C A191999 See A191998. %F A191999 a(n) = denominator(r(n)) with %F A191999 r(n):=product(1-Chi_2(4;p(j))/(p(j)-1),j=1..n), n>=1, with the primes p(j)=A000040(j) and the nontrivial Dirichlet Character modulo 4, called here Chi_2(4;k) = A056594(k). %e A191999 The rationals r(n) are: 1, 3/2, 9/8, 21/16, 231/160, 847/640, 2541/2048, ... %Y A191999 Cf. A191998, A191996/A191997. %K A191999 nonn,easy,frac %O A191999 1,2 %A A191999 _Wolfdieter Lang_, Jun 21 2011