|
%I #13 Mar 23 2021 05:18:52
%S 1,2,3,4,5,7,9,11,12,13,14,16,17,19,23,25,29,31,33,37,41,43,45,47,53,
%T 57,59,61,67,71,73,79,83,85,89,97,101,103,107,109,113,127,131,137,139,
%U 149,151,157,159,163,167,169,173,175,179,181,191,193,197,199,211,216,223
%N Numbers k for which the cototient k - phi(k) is a Fibonacci number.
%H Amiram Eldar, <a href="/A117290/b117290.txt">Table of n, a(n) for n = 1..10000</a>
%e 33 is in the sequence because 33 - phi(33) = 13, which is a Fibonacci number.
%t With[{fibs=Fibonacci[Range[0, 13]]},Select[Range[fibs[[-1]]],MemberQ[fibs,#-EulerPhi[#]]&]] (* _Harvey P. Dale_, Jan 28 2011 *)
%o (PARI) isfib(n) = my(k=n^2); k+=(k+1)<<2; issquare(k) || (n>0 && issquare(k-8));
%o isok(n) = isfib(n-eulerphi(n)); \\ _Michel Marcus_, Mar 23 2021
%Y Cf. A000010, A000045, A051953.
%K nonn
%O 1,2
%A Luc Stevens (lms022(AT)yahoo.com), Apr 23 2006
%E Offset corrected and a(1) added by _Amiram Eldar_, Mar 23 2021
|
