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A067786
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Numbers n such that phi(n) = 2*pi(n) where pi(n) = A000720(n) and phi(n) = A000010(n).
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0
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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
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1,1
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COMMENTS
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There are no more terms < 10^10. Conjectured to be complete. - Donovan Johnson, Nov 24 2013
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LINKS
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EXAMPLE
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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.
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MATHEMATICA
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Select[Range[500000], 2PrimePi[#] == EulerPhi[#] &] (* Harvey P. Dale, Nov 22 2013 *)
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PROG
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(PARI) isok(n) = eulerphi(n) == 2*primepi(n); \\ Michel Marcus, Nov 22 2013
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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