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 A015734 #11 May 15 2024 01:30:05 %S A015734 25,27,75,81,121,189,225,275,289,297,343,363,405,425,513,529,567,575, %T A015734 605,621,725,729,825,837,841,867,1025,1029,1053,1089,1161,1175,1225, %U A015734 1269,1275,1325,1331,1377,1445,1475,1539,1587,1593,1681,1725 %N A015734 Odd numbers k such that d(k) does not divide phi(k). %H A015734 Amiram Eldar, <a href="/A015734/b015734.txt">Table of n, a(n) for n = 1..10000</a> %t A015734 Select[Range[1, 2000, 2], !Divisible[EulerPhi[#], DivisorSigma[0, #]] &] (* _Amiram Eldar_, May 15 2024 *) %o A015734 (PARI) is(k) = if(k%2, my(f = factor(k), d = numdiv(f), p = eulerphi(f)); p % d, 0); \\ _Amiram Eldar_, May 15 2024 %Y A015734 Intersection of A005408 and A015733. %Y A015734 Cf. A000005 (d), A000010 (phi). %K A015734 nonn %O A015734 1,1 %A A015734 _Robert G. Wilson v_ %E A015734 Offset corrected by _Amiram Eldar_, May 15 2024