A117283 - OEIS

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A117283

Numbers k for which the cototient k-phi(k) is a cube.

1, 2, 3, 5, 7, 11, 12, 13, 14, 16, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 63, 67, 71, 73, 79, 81, 83, 89, 96, 97, 101, 103, 107, 109, 112, 113, 115, 124, 127, 128, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 187, 191, 193, 197, 199, 211, 223, 227

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

LINKS

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

EXAMPLE

63 is in the sequence because 63-phi(63) = 27, which is a cube.

MATHEMATICA

Select[Range[230], IntegerQ[(# - EulerPhi[ # ])^(1/3)] &] (* Stefan Steinerberger, Apr 24 2006 *)

PROG

(PARI) isok(k) = ispower(k-eulerphi(k), 3); \\ Michel Marcus, Mar 23 2021

CROSSREFS