A015734 Odd numbers k such that d(k) does not divide phi(k).

25, 27, 75, 81, 121, 189, 225, 275, 289, 297, 343, 363, 405, 425, 513, 529, 567, 575, 605, 621, 725, 729, 825, 837, 841, 867, 1025, 1029, 1053, 1089, 1161, 1175, 1225, 1269, 1275, 1325, 1331, 1377, 1445, 1475, 1539, 1587, 1593, 1681, 1725

Offset: 1

Author

Robert G. Wilson v

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Intersection of A005408 and A015733.

Cf. A000005 (d), A000010 (phi).

Programs

Mathematica

Select[Range[1, 2000, 2], !Divisible[EulerPhi[#], DivisorSigma[0, #]] &] (* Amiram Eldar, May 15 2024 *)

PARI

is(k) = if(k%2, my(f = factor(k), d = numdiv(f), p = eulerphi(f)); p % d, 0); \\ Amiram Eldar, May 15 2024

Extensions

Offset corrected by Amiram Eldar, May 15 2024