A353685 Numbers k for which phi(sigma(k)) <= phi(k).

1, 3, 5, 7, 11, 13, 15, 17, 19, 23, 26, 27, 29, 31, 33, 35, 37, 38, 39, 41, 43, 45, 47, 49, 51, 53, 55, 57, 58, 59, 61, 65, 67, 69, 71, 73, 74, 77, 79, 82, 83, 85, 86, 87, 89, 91, 95, 97, 99, 101, 103, 104, 107, 109, 111, 113, 115, 116, 117, 118, 119, 121, 122, 123, 125, 127, 129, 131, 133, 134, 135, 137, 139, 141, 143

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

Cf. A000010, A000203, A062401, A353683 (complement).

Positions of zeros in A353681. Positions of terms <= 0 in A353636.

Disjoint union of A006872 and A353686.

Programs

Mathematica

Select[Range[150], EulerPhi[DivisorSigma[1, #]] <= EulerPhi[#] &] (* Amiram Eldar, May 06 2022 *)

PARI

isA353685(n) = (eulerphi(sigma(n))<=eulerphi(n));