

A067786


Numbers n such that phi(n) = 2*pi(n) where pi(n) = A000720(n) and phi(n) = A000010(n).


0



11, 13, 27, 39, 63, 122, 124, 136, 152, 176, 224, 322, 364, 410, 460, 1086, 1164, 3432, 3612, 12012
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OFFSET

1,1


COMMENTS

Next term > 10^6.  Michel Marcus, Nov 22 2013
There are no more terms < 10^10. Conjectured to be complete.  Donovan Johnson, Nov 24 2013


LINKS

Table of n, a(n) for n=1..20.


EXAMPLE

pi(11) = 5 and phi(11) = 10, so 11 is in the sequence.
pi(12) = 5 but phi(12) = 4, so 12 is not in the sequence.
pi(13) = 6 and phi(13) = 12, so 13 is in the sequence.


MATHEMATICA

Select[Range[500000], 2PrimePi[#] == EulerPhi[#] &] (* Harvey P. Dale, Nov 22 2013 *)


PROG

(PARI) isok(n) = eulerphi(n) == 2*primepi(n); \\ Michel Marcus, Nov 22 2013


CROSSREFS

Sequence in context: A295340 A153055 A146915 * A132245 A140567 A232880
Adjacent sequences: A067783 A067784 A067785 * A067787 A067788 A067789


KEYWORD

nonn


AUTHOR

Benoit Cloitre, Feb 06 2002


EXTENSIONS

Corrected and extended by Michel Marcus, Nov 22 2013
Confirmed by Harvey P. Dale, Nov 22 2013


STATUS

approved



