A353683 Numbers k for which phi(sigma(k)) > phi(k).

2, 4, 6, 8, 9, 10, 12, 14, 16, 18, 20, 21, 22, 24, 25, 28, 30, 32, 34, 36, 40, 42, 44, 46, 48, 50, 52, 54, 56, 60, 62, 63, 64, 66, 68, 70, 72, 75, 76, 78, 80, 81, 84, 88, 90, 92, 93, 94, 96, 98, 100, 102, 105, 106, 108, 110, 112, 114, 120, 124, 126, 128, 130, 132, 136, 138, 140, 142, 144, 148, 150, 152, 154, 156, 160

Offset: 1

Author

Antti Karttunen, May 06 2022

Keywords

• nonn

Comments

Numbers k such that A062401(k) > A000010(k).

Links

• Index entries for sequences related to sigma(n)

Crossrefs

Positions of strictly positive terms in A353636.

Cf. A000010, A000203, A062401, A353681 (characteristic function), A353685 (complement).

Setwise difference of A353684 and A006872.

Programs

Mathematica

Select[Range[160], EulerPhi[DivisorSigma[1, #]] > EulerPhi[#] &] (* Amiram Eldar, May 06 2022 *)

PARI

A353681(n) = (eulerphi(sigma(n))>eulerphi(n));
isA353683(n) = A353681(n);