A117283 - OEIS

%I #11 Mar 23 2021 05:20:20

%S 1,2,3,5,7,11,12,13,14,16,17,19,23,29,31,37,41,43,47,53,59,61,63,67,

%T 71,73,79,81,83,89,96,97,101,103,107,109,112,113,115,124,127,128,131,

%U 137,139,149,151,157,163,167,173,179,181,187,191,193,197,199,211,223,227

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

%H Amiram Eldar, <a href="/A117283/b117283.txt">Table of n, a(n) for n = 1..10000</a>

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

%t Select[Range[230], IntegerQ[(# - EulerPhi[ # ])^(1/3)] &] (* _Stefan Steinerberger_, Apr 24 2006 *)

%o (PARI) isok(k) = ispower(k-eulerphi(k), 3); \\ _Michel Marcus_, Mar 23 2021

%Y Cf. A000010, A000578, A051953.

%Y Cf. A117284, A117285, A117286, A117287, A117288, A117289.

%K nonn

%O 1,2

%A Luc Stevens (lms022(AT)yahoo.com), Apr 23 2006