A043343 Numbers m such that there is no k > m such that phi(k) = phi(m), where phi is Euler's totient function.

2, 6, 12, 18, 22, 30, 42, 46, 54, 58, 60, 62, 66, 90, 94, 98, 106, 118, 120, 126, 134, 138, 142, 150, 158, 162, 166, 174, 198, 206, 210, 214, 240, 242, 250, 254, 262, 270, 274, 276, 278, 282, 294, 298, 302, 318, 330, 334, 346, 348, 354, 358, 378, 382, 394, 398

Offset: 1

Author

Vladeta Jovovic, Jan 12 2002

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..980 from Paul Tek)
• Max Alekseyev, PARI/GP Scripts for Miscellaneous Math Problems (invphi.gp).

Crossrefs

Cf. A000010, A028476, A066659.

Programs

Mathematica

Flatten@ Position[#, 0] &@ Table[k = n + 1; While[And[k <= 2 n + 1, EulerPhi@ k != EulerPhi@ n], k++]; Boole[k < 2 n + 1] k, {n, 400}] (* Michael De Vlieger, Dec 31 2016 *)

PARI

is(k) = #select(x -> x>k, invphi(eulerphi(k))) == 0; \\ Amiram Eldar, Nov 12 2024, using Max Alekseyev's invphi.gp

Formula

A066659(a(n)) = 0.

A028476(a(n)) = a(n).

Extensions

Offset corrected by Paul Tek, Sep 25 2015

Definition clarified by Alonso del Arte, Dec 31 2016