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 A090395 #28 Jun 20 2022 14:45:19
%S A090395 1,1,3,4,5,3,7,2,3,5,11,2,13,7,15,16,17,3,19,10,21,11,23,3,25,13,27,
%T A090395 14,29,15,31,16,33,17,35,4,37,19,39,5,41,21,43,22,15,23,47,24,49,25,
%U A090395 51,26,53,27,55,7,57,29,59,5,61,31,21,64,65,33,67,34,69,35,71,6,73,37,25,38
%N A090395 Denominator of d(n)/n, where d(n) is the number of divisors of n (A000005).
%C A090395 The first occurrence of k (if it exists) is studied in A091895.
%C A090395 Sequence A353011 gives indices of "late birds": n such that a(k) > a(n) for all k > n. - _M. F. Hasler_, Apr 15 2022
%H A090395 Antti Karttunen, <a href="/A090395/b090395.txt">Table of n, a(n) for n = 1..65537</a>
%F A090395 a(n) = n/g with g = A009191(n) = gcd(A000005(n), n). This explains the "rays" in the graph, e.g., g = 1 for odd squarefree n, g = 2 for even semiprimes n = 2p > 4 and n = 4p, p > 3. - _M. F. Hasler_, Apr 15 2022
%e A090395 a(6) = 3 because the number of divisors of 6 is 4 and 4 divided by 6 equals 2/3, which has 3 as its denominator.
%p A090395 with(numtheory): seq(denom(tau(n)/n), n=1..75) ; # _Zerinvary Lajos_, Jun 04 2008
%t A090395 Table[ Denominator[ DivisorSigma[0, n]/n], {n, 1, 80}] (* _Robert G. Wilson v_, Feb 04 2004 *)
%o A090395 (PARI) A090395(n) = denominator(numdiv(n)/n); \\ _Antti Karttunen_, Sep 25 2018
%o A090395 (Python)
%o A090395 from math import gcd
%o A090395 from sympy import divisor_count
%o A090395 def A090395(n): return n//gcd(n,divisor_count(n)) # _Chai Wah Wu_, Jun 20 2022
%Y A090395 Cf. A000005, A090387 (numerators), A091896 (numbers not in this sequence), A353011 (indices of terms such that all subsequent terms are larger).
%K A090395 easy,frac,nonn
%O A090395 1,3
%A A090395 Ivan_E_Mayle(AT)a_provider.com, Jan 31 2004
%E A090395 More terms from _Robert G. Wilson v_, Feb 04 2004