A039743 Number k such that gcd(phi(k), k-1) = number of distinct prime factors of k.

2, 4, 8, 15, 16, 32, 35, 39, 51, 55, 63, 64, 70, 75, 87, 95, 99, 111, 115, 119, 123, 128, 130, 135, 143, 147, 154, 155, 159, 171, 183, 187, 203, 207, 215, 219, 235, 238, 256, 267, 275, 279, 280, 287, 291, 295, 299, 303, 310, 319, 322, 323, 327, 335, 339, 351

Offset

1,1

Comments

Number of primes counted without multiplicity. - Harvey P. Dale, Jun 19 2020

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Example

phi(15) = 8, gcd(8, 14) = 2, 15 = 3*5, 2 prime factors.

Mathematica

Select[Range[400], GCD[EulerPhi[#], #-1]==PrimeNu[#]&] (* Harvey P. Dale, Jun 19 2020 *)

Prog

(PARI) is(k) = k > 1 && gcd(eulerphi(k), k-1) == omega(k); \\ Amiram Eldar, Sep 18 2024

Crossrefs

Cf. A000010, A001221.

Sequence in context: A076351 A140117 A328677 * A070008 A033623 A094398

Adjacent sequences: A039740 A039741 A039742 * A039744 A039745 A039746

Keyword

nonn,easy

Author

Olivier Gérard

Extensions

Definition clarified by Harvey P. Dale, Jun 19 2020

Status

approved