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 A386402 #10 Jul 21 2025 08:56:57
%S A386402 1,4,9,8,25,3,49,16,27,25,121,9,169,49,75,32,289,18,361,25,147,121,
%T A386402 529,6,125,169,81,7,841,25,961,64,363,289,1225,108,1369,361,507,10,
%U A386402 1681,49,1849,121,225,529,2209,36,343,125,289,169,2809,27,605,49,361,841,3481,75
%N A386402 a(n) = denominator(sigma(n)*phi(n)/n^2).
%C A386402 A386401(n)/a(n) = sigma(n)*phi(n)/n^2 is a multiplicative function since it is the product of three multiplicative functions.
%D A386402 James J. Tattersall, Elementary Number Theory in Nine Chapters, Cambridge University Press, 1999, Exercise 5.3.21 on page 169.
%H A386402 Amiram Eldar, <a href="/A386402/b386402.txt">Table of n, a(n) for n = 1..10000</a>
%t A386402 a[n_]:=Denominator[DivisorSigma[1,n]EulerPhi[n]/n^2]; Array[a,60]
%o A386402 (PARI) a(n) = {my(f = factor(n)); denominator(sigma(f) * eulerphi(f) / n^2);} \\ _Amiram Eldar_, Jul 21 2025
%Y A386402 Cf. A000010, A000203, A000290.
%Y A386402 Cf. A386401 (numerators).
%K A386402 nonn,easy,frac
%O A386402 1,2
%A A386402 _Stefano Spezia_, Jul 20 2025