A066659 Least k > n such that phi(k) = phi(n), if such k exists; = 0 otherwise.

2, 0, 4, 6, 8, 0, 9, 10, 14, 12, 22, 0, 21, 18, 16, 20, 32, 0, 27, 24, 26, 0, 46, 30, 33, 28, 38, 36, 58, 0, 62, 34, 44, 40, 39, 42, 57, 54, 45, 48, 55, 0, 49, 50, 52, 0, 94, 60, 86, 66, 64, 56, 106, 0, 75, 70, 63, 0, 118, 0, 77, 0, 74, 68, 104, 0, 134, 80, 92, 72, 142, 78, 91

Offset: 1

Author

Joseph L. Pe, Jan 10 2002

Keywords

• nonn

Links

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

Crossrefs

Cf. A000010, A043343.

Programs

Mathematica

Table[k = n + 1; While[And[k <= 2 n + 1, EulerPhi@ k != EulerPhi@ n], k++]; Boole[k < 2 n + 1] k, {n, 73}] (* Michael De Vlieger, Dec 31 2016 *)

PARI

a(n) = {my(v = select(x -> x>n, invphi(eulerphi(n)))); if(#v == 0, 0, vecmin(v));} \\ Amiram Eldar, Nov 14 2024, using Max Alekseyev's invphi.gp

Extensions

More terms from Vladeta Jovovic, Jan 12 2002

Typo in data fixed by Paul Tek, Sep 20 2015