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

1,1

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).

Formula

A066659(a(n)) = 0.

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

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 *)

Prog

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

Crossrefs

Cf. A000010, A028476, A066659.

Sequence in context: A263269 A262503 A263082 * A066080 A319270 A071707

Adjacent sequences: A043340 A043341 A043342 * A043344 A043345 A043346

Keyword

nonn

Author

Vladeta Jovovic, Jan 12 2002

Extensions

Offset corrected by Paul Tek, Sep 25 2015

Definition clarified by Alonso del Arte, Dec 31 2016

Status

approved