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 A353643 #12 May 07 2022 09:42:42 %S A353643 1,1,2,2,2,2,2,4,6,2,2,4,6,2,8,2,2,6,2,4,4,2,2,8,10,12,2,12,4,8,2,4,4, %T A353643 2,8,12,18,2,24,8,4,4,2,4,24,2,2,4,6,20,8,6,2,2,8,8,4,4,2,16,30,2,12, %U A353643 2,24,4,2,4,4,24,2,24,36,36,20,12,4,24,2,4,2,4,2,24,4,2,8,8,8,24,24,4,4,2,8,8,6,6 %N A353643 The greatest common divisor of phi(n) and phi(sigma(n)). %H A353643 Antti Karttunen, <a href="/A353643/b353643.txt">Table of n, a(n) for n = 1..16384</a> %H A353643 Antti Karttunen, <a href="/A353643/a353643.txt">Data supplement: n, a(n) computed for n = 1..65537</a> %H A353643 <a href="/index/Si#SIGMAN">Index entries for sequences related to sigma(n)</a> %F A353643 a(n) = gcd(A000010(n), A062401(n)). %F A353643 a(n) = gcd(A000010(n), A353636(n)) = gcd(A062401(n), A353636(n)). %F A353643 a(n) = A000010(n) / A353644(n). %F A353643 a(n) = A062401(n) / A353646(n). %t A353643 a[n_] := GCD[EulerPhi[n], EulerPhi[DivisorSigma[1, n]]]; Array[a, 100] (* _Amiram Eldar_, May 06 2022 *) %o A353643 (PARI) A353643(n) = gcd(eulerphi(sigma(n)), eulerphi(n)); %Y A353643 Cf. A000010, A000203, A062401, A353636, A353644, A353646. %K A353643 nonn %O A353643 1,3 %A A353643 _Antti Karttunen_, May 06 2022