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 A166123 #15 Aug 02 2019 23:00:37
%S A166123 1,1,1,1,1,1,1,1,3,1,1,1,1,1,3,1,1,1,1,1,3,1,1,1,5,1,3,1,1,1,1,1,3,1,
%T A166123 1,1,1,1,3,1,1,1,1,1,15,1,1,1,7,1,3,1,1,1,1,1,3,1,1,1,1,1,3,1,5,1,1,1,
%U A166123 3,1,1,1,1,1,3,1,1,1,1,1,3,1,1,1,5,1,3,1,1,1,7,1,3,1,1,1,1,1,3,1
%N A166123 If n is prime, a(n) = 1; otherwise, a(n) is gcd(n, d) where d is the denominator of the (n-1)-th Bernoulli number.
%H A166123 Antti Karttunen, <a href="/A166123/b166123.txt">Table of n, a(n) for n = 1..21218</a>
%F A166123 a(n) = A166120(n)/ A050932(n-1).
%t A166123 Table[If[PrimeQ[n],1,GCD[n,Denominator[BernoulliB[n-1]]]],{n,100}] (* _Harvey P. Dale_, Sep 07 2017 *)
%o A166123 (PARI) a(n)=if(isprime(n),1,gcd(denominator(bernfrac(n-1)),n)) \\ _Charles R Greathouse IV_, Jun 20 2011
%o A166123 (PARI) a(n)=my(b=bernfrac(n-1));denominator(b)/denominator(b*n)/if(isprime(n),n,1) \\ _Charles R Greathouse IV_, Jun 20 2011
%o A166123 (PARI) a(n)=if(isprime(n),1,my(b=bernfrac(n-1));denominator(b)/denominator(b*n)) \\ _Charles R Greathouse IV_, Jun 20 2011
%Y A166123 Cf. A166062, A027642.
%K A166123 nonn
%O A166123 1,9
%A A166123 _Paul Curtz_, Oct 07 2009