A066705 Greatest k < n such that phi(k) = phi(n) if such k exists, otherwise 0.

0, 1, 0, 3, 0, 4, 0, 5, 7, 8, 0, 10, 0, 9, 0, 15, 0, 14, 0, 16, 13, 11, 0, 20, 0, 21, 19, 26, 0, 24, 0, 17, 25, 32, 0, 28, 0, 27, 35, 34, 0, 36, 0, 33, 39, 23, 0, 40, 43, 44, 0, 45, 0, 38, 41, 52, 37, 29, 0, 48, 0, 31, 57, 51, 0, 50, 0, 64, 0, 56, 0, 70, 0, 63, 55, 74, 61, 72, 0, 68, 0

Offset: 1

Author

Vladeta Jovovic, Jan 14 2002

Keywords

• nonn

Links

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

Crossrefs

Cf. A000010, A015126, A028476, A043343, A066659.

Programs

PARI

a(n) = {my(v = select(x -> xAmiram Eldar, Nov 14 2024, using Max Alekseyev's invphi.gp