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 A081396 #16 Jan 22 2020 20:08:45
%S A081396 0,0,1,0,1,1,1,0,0,1,1,1,1,2,1,0,1,1,1,1,1,1,1,1,0,2,1,1,1,1,1,0,1,1,
%T A081396 2,0,1,2,1,1,1,2,1,1,2,1,1,1,1,0,1,1,1,2,1,2,1,1,1,1,1,2,1,0,2,1,1,1,
%U A081396 1,2,1,1,1,2,1,1,2,2,1,1,0,1,1,1,1,2,1,2,1,2,1,1,1,1,2,1,1,1,2,0,1,1,1,2,2
%N A081396 Number of common prime factors (ignoring multiplicity) of sigma(n) = A000203(n) and phi(n) = A000010(n).
%H A081396 Antti Karttunen, <a href="/A081396/b081396.txt">Table of n, a(n) for n = 1..65537</a>
%F A081396 a(n) = A001221(A009223(n)). - _Antti Karttunen_, Jan 22 2020
%e A081396 n=209: sigma(209) = 240 = 2*2*2*2*3*5, phi(209) = 180 = 2*2*3*3*5, common factor set = {2,3,5}, so a(209)=3.
%t A081396 ffi[x_] := Flatten[FactorInteger[x]] lf[x_] := Length[FactorInteger[x]] ba[x_] := Table[Part[ffi[x], 2*w-1], {w, 1, lf[x]}] Table[Length[Intersection[ba[EulerPhi[w]], ba[DivisorSigma[1, w]]]], {w, 1, 100}]
%o A081396 (PARI) a(n)=omega(gcd(sigma(n),eulerphi(n))) \\ _Charles R Greathouse IV_, Feb 19 2013
%Y A081396 Cf. A000010, A000203, A001221, A009223, A081383, A082055.
%K A081396 nonn
%O A081396 1,14
%A A081396 _Labos Elemer_, Mar 28 2003
%E A081396 Data section extended up to a(105) by _Antti Karttunen_, Jan 22 2020