A050472 Numbers m such that 2*phi(m) = phi(m+1).

2, 4, 16, 154, 256, 286, 364, 804, 1066, 2146, 3382, 4550, 6106, 7700, 8176, 9268, 11284, 12556, 12970, 16402, 19228, 19276, 20272, 25132, 26404, 27346, 29154, 29574, 35644, 36418, 38368, 39646, 40494, 47214, 52234, 54652, 65536, 84862

Offset

1,1

References

R. K. Guy, Unsolved Problems Number Theory, Sect. B36.

Links

Giovanni Resta, Table of n, a(n) for n = 1..10000 (first 1000 terms from Donovan Johnson)

Formula

Conjecture : a(n)/n^3 is bounded. Does lim n -> infinity a(n)/n^3 = 2 ? - Benoit Cloitre, Aug 07 2002

a(n) = A171271(n) - 1. - Ray Chandler, May 01 2015

Example

phi(256)=128, phi(256+1)=2*128, so 256 is a member of the sequence.

Prog

(PARI) isok(n) = 2*eulerphi(n) == eulerphi(n+1); \\ Michel Marcus, Aug 02 2018

Crossrefs

Cf. A000010, A001274, A050473, A171271.

Sequence in context: A362065 A061588 A202360 * A109457 A352801 A105788

Adjacent sequences: A050469 A050470 A050471 * A050473 A050474 A050475

Keyword

nonn

Author

Jud McCranie, Dec 24 1999

Status

approved