A353684 Numbers k for which phi(sigma(k)) >= phi(k).

1, 2, 3, 4, 6, 8, 9, 10, 12, 14, 15, 16, 18, 20, 21, 22, 24, 25, 26, 28, 30, 32, 34, 36, 39, 40, 42, 44, 45, 46, 48, 50, 52, 54, 56, 60, 62, 63, 64, 66, 68, 70, 72, 74, 75, 76, 78, 80, 81, 84, 88, 90, 92, 93, 94, 96, 98, 100, 102, 104, 105, 106, 108, 110, 111, 112, 114, 117, 120, 122, 124, 126, 128, 130, 132, 136, 138

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 nonnegative terms in A353636.

Cf. A000010, A000203, A062401, A353682 (characteristic function), A353686 (complement).

Disjoint union of A006872 and A353683.

Programs

Mathematica

Select[Range[140], EulerPhi[DivisorSigma[1, #]] >= EulerPhi[#] &] (* Amiram Eldar, May 06 2022 *)

PARI

A353682(n) = (eulerphi(sigma(n))>=eulerphi(n));
isA353684(n) = A353682(n);