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A062699
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Numbers n such that sigma(n)=phi(n)*2.
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19
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3, 35, 1045, 24871, 29029, 50065, 58435, 64285, 87685, 137885, 140335, 1390753, 1529983, 1739507, 2011009, 2086903, 3189625, 3281663, 3501605, 3722875, 3830827, 3852155, 6605945, 7711405, 8409305, 9815195
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| 3 is the only prime term of this sequence. There is no term of the form p^k where p is a prime and k>1. All terms are odd because if n is even then 2*phi(n)=phi(2n)<=n<sigma(n). - Farideh Firoozbakht (mymontain(AT)yahoo.com), Apr 01 2005, Feb 24 2007
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LINKS
| Harry J. Smith, Table of n, a(n) for n=1,...,50
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PROG
| (PARI) for(n=1, 500000, if(sigma(n)==eulerphi(n)*2, print(n)))
(PARI) { n=0; for (m=1, 10^9, if(sigma(m)==2*eulerphi(m), write("b062699.txt", n++, " ", m); if (n==50, break)) ) } [From Harry J. Smith (hjsmithh(AT)sbcglobal.net), Aug 09 2009]
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CROSSREFS
| Cf. A068390, A104900, A104901.
Sequence in context: A185752 A135516 A107712 * A012767 A136525 A136556
Adjacent sequences: A062696 A062697 A062698 * A062700 A062701 A062702
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KEYWORD
| nonn
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AUTHOR
| Jason Earls (zevi_35711(AT)yahoo.com), Jul 11 2001
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EXTENSIONS
| More terms from Labos E. (labos(AT)ana.sote.hu), Nov 23 2001
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