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 A201059 #20 Jan 12 2024 07:56:42
%S A201059 1,2,3,4,5,1,7,8,9,5,11,6,13,7,1,16,17,3,19,2,7,11,23,4,25,13,27,1,29,
%T A201059 15,31,32,11,17,5,18,37,19,39,4,41,1,43,11,1,23,47,8,49,25,17,13,53,9,
%U A201059 55,14,19,29,59,5,61,31,21,64,13,1,67,34,23,7,71,4,73,37,5
%N A201059 Denominator of binomial(2n,n)/(2n).
%C A201059 There is at least one published paper that refers to binomial(2n,n)/(2n) as the Catalan numbers. Of course the Catalan numbers are really A000108.
%H A201059 David A. Corneth, <a href="/A201059/b201059.txt">Table of n, a(n) for n = 1..10000</a>
%H A201059 Patrick Dehornoy, <a href="http://dx.doi.org/10.1016/j.aim.2009.09.016">On the rotation distance between binary trees</a>, Adv. Math. 223 (2010), no. 4, 1316-1355.
%e A201059 1, 3/2, 10/3, 35/4, 126/5, 77, 1716/7, 6435/8, 24310/9, 46189/5, 352716/11, 676039/6, ...
%t A201059 Table[Denominator[Binomial[2n,n]/(2n)],{n,50}] (* _Harvey P. Dale_, Oct 04 2021 *)
%o A201059 (PARI) a(n) = denominator(binomial(2*n,n)/(2*n)); \\ _Michel Marcus_, Jan 08 2024
%o A201059 (PARI) a(n) = my(f = factor(2*n), res = 1); for(i = 1, #f~, v = val(2*n, f[i,1]) - 2*val(n, f[i, 1]) - f[i, 2]; if(v < 0, res*=f[i, 1]^(-v))); res
%o A201059 val(n, p) = my(r=0); while(n, r+=n\=p); r \\ _David A. Corneth_, Jan 10 2024
%Y A201059 Cf. A000108, A201058, A268082.
%K A201059 nonn,frac
%O A201059 1,2
%A A201059 _N. J. A. Sloane_, Nov 26 2011
%E A201059 More terms from _Michel Marcus_, Jan 08 2024