A333407 Numbers k such that phi(k) = phi(2*k-1) where phi is the Euler totient function (A000010).

1, 1313, 1853, 6683, 12773, 28823, 194123, 198743, 343493, 702923, 829793, 1309853, 1379963, 1846763, 2001203, 2788913, 3911603, 5399363, 5464463, 5689373, 10728113, 11316143, 11776853, 12082073, 14588213, 16587383, 19610063, 20294243, 21470963, 25388963, 28433903

Offset

1,2

Links

Amiram Eldar, Table of n, a(n) for n = 1..100

Example

1313 is a term since 1313 and 2*1313 - 1 = 2625 have the same value of phi: phi(1313) = phi(2625) = 1200.

Mathematica

seq = {}; Do[If[EulerPhi[n] == EulerPhi[2*n-1], AppendTo[seq, n]], {n, 1, 10^5}]; seq

Prog

(PARI) isok(k) = eulerphi(k) == eulerphi(2*k-1); \\ Michel Marcus, Mar 20 2020

Crossrefs

Cf. A000010, A092272.

Sequence in context: A030646 A223612 A223413 * A221155 A237393 A242151

Adjacent sequences: A333404 A333405 A333406 * A333408 A333409 A333410

Keyword

nonn

Author

Amiram Eldar, Mar 19 2020

Status

approved