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 A098512 #14 Mar 04 2018 21:17:44 %S A098512 1,1,1,5,7,42,22,429,715,4862,8398,58786,52003,742900,1337220,646323, %T A098512 17678835,129644790,79606450,1767263190,328206021,8155422340, %U A098512 45741281820,343059613650,107492012277,4861946401452,9183676536076 %N A098512 Second column and subdiagonal of number triangle A098509. %F A098512 a(n) = denominator(n(n+1)/binomial(2n, n)). %F A098512 a(n) = denominator(n/C(n)). - _Paul Barry_, Nov 17 2004 %F A098512 a(n) = C(n) / gcd(n, C(n)). - _Peter Luschny_, Oct 06 2011 %p A098512 C := n -> binomial(2*n,n)/(n+1): %p A098512 A098512 := n -> C(n)/igcd(n,C(n)): # _Peter Luschny_, Oct 06 2011 %Y A098512 Cf. A093526, A093527, A000108. %K A098512 easy,nonn %O A098512 0,4 %A A098512 _Paul Barry_, Sep 11 2004