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

1,4

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Max Alekseyev, PARI/GP Scripts for Miscellaneous Math Problems (invphi.gp).

Prog

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

Crossrefs

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

Sequence in context: A363028 A364067 A246691 * A277894 A027636 A371737

Adjacent sequences: A066702 A066703 A066704 * A066706 A066707 A066708

Keyword

nonn

Author

Vladeta Jovovic, Jan 14 2002

Status

approved