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 A073809 #16 Nov 26 2017 05:28:05
%S A073809 1,2,3,1,4,6,4,4,1,6,6,6,4,8,8,2,6,2,6,8,6,9,8,12,1,8,8,4,8,12,6,3,10,
%T A073809 8,10,1,4,12,8,12,8,12,6,6,4,12,10,6,2,2,12,4,8,16,12,16,10,12,12,16,
%U A073809 4,12,4,2,12,15,6,12,12,15,12,8,4,8,3,12,12,16,10,8,3,12,12,12,12,12,16
%N A073809 Number of common divisors of sigma_1(n) and sigma_3(n).
%H A073809 Antti Karttunen, <a href="/A073809/b073809.txt">Table of n, a(n) for n = 1..16384</a>
%F A073809 a(n) = Card[Intersection[D[A000203(n)], D[A001158(n)]]] where D[x] is the set of divisors of x.
%e A073809 n=10: sigma[1,10]=18, sigma[3,10]=1134; Intersection[{1,2,3,6,9,18},{1,2,3,6,7,9,14,18,21,27,42,54,63, 81,126,162,189,378,567,1134}]={1,2,3,6,9,18}, so a(10)=6.
%t A073809 g1[x_] := Divisors[DivisorSigma[1, x]] g2[x_] := Divisors[DivisorSigma[3, x]] ncd[x_] := Length[Intersection[g1[x], g2[x]]] Table[ncd[w], {w, 1, 128}]
%t A073809 (* Second program: *)
%t A073809 Table[Length@ Apply[Intersection, Divisors@ Array[DivisorSigma[2 # - 1, n] &, 2]], {n, 87}] (* _Michael De Vlieger_, Nov 23 2017 *)
%o A073809 (PARI) A073809(n) = numdiv(gcd(sigma(n),sigma(n,3))); \\ _Antti Karttunen_, Nov 23 2017
%Y A073809 Cf. A000203, A001158, A073802, A073808.
%K A073809 nonn
%O A073809 1,2
%A A073809 _Labos Elemer_, Aug 13 2002