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 A195686 #25 Aug 06 2022 19:06:57
%S A195686 1,2,3,20,35,252,154,3432,6435,48620,92378,705432,676039,10400600,
%T A195686 20058300,10341168,300540195,2333606220,1512522550,35345263800,
%U A195686 6892326441,179419291480,1052049481860,8233430727600,2687300306925,126410606437752,247959266474052
%N A195686 a(n) = C(2*n,n) / gcd(n,C(2*n,n)).
%H A195686 T. D. Noe, <a href="/A195686/b195686.txt">Table of n, a(n) for n = 0..400</a>
%F A195686 A093526(n) = a(n+1)/(n+2).
%F A195686 a(n) = numerator(C(2n,n)/n). - _Enrique Pérez Herrero_, Mar 26 2012
%F A195686 Sum_{n>=0} A093527(n)/a(n+1) = Sum_{n>=1} n/binomial(2*n,n) = 2/3 + 2*Pi/(9*sqrt(3)) (A145429). - _Amiram Eldar_, Jan 26 2022
%F A195686 a(n) = numerator((n + 1)*binomial(2*n+1, n)/(n*(2*n + 1))) for n > 0. - _Stefano Spezia_, Aug 06 2022
%p A195686 A195686 := n -> binomial(2*n,n)/igcd(n,binomial(2*n,n));
%t A195686 a[n_] := Numerator[Binomial[2n,n]/n]; Join[{1}, Table[a[n], {n, 100}]] (* _Enrique Pérez Herrero_, Mar 26 2012 *)
%Y A195686 Cf. A093526, A093527, A145429.
%K A195686 nonn
%O A195686 0,2
%A A195686 _Peter Luschny_, Oct 06 2011