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A066881
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Numbers n such that sigma(phi(n))/sigma(n) is an integer >= 4.
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2
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121679, 1043909, 2350171, 2918263, 3396103, 3566807, 3688067, 4019467, 4562827, 5963407, 7300697, 7485979, 7853933, 8103301, 8364151, 9237779, 9514213, 9638527, 10531123, 11094619, 11384447, 12721937, 13576267, 15331313
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| Conjecture: all natural numbers 1,2,3,..n will eventually occur among the integer values of sigma(phi(n))/sigma(n).
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LINKS
| Harry J. Smith, Table of n, a(n) for n=1,...,370
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EXAMPLE
| a(1)=121679 because sigma(phi(121679))/sigma(121679) = 4.
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MAPLE
| for n from 1 do spn := numtheory[sigma](numtheory[phi](n)) ; sn := numtheory[sigma](n) ; if spn mod sn = 0 then if spn/sn >= 4 then print(n, spn/sn) fi; fi; od: [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Oct 01 2008]
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PROG
| (PARI) { n=0; for (m=1, 10^10, if((e=sigma(eulerphi(m))) % (s=sigma(m)) == 0 && e/s >= 4, write("b066881.txt", n++, " ", m); if (n==1000, return)) ) } [From Harry J. Smith (hjsmithh(AT)sbcglobal.net), Apr 03 2010]
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CROSSREFS
| Cf. A066817.
Cf. A067383, A067382. [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Oct 01 2008]
Sequence in context: A068136 A135495 A067384 * A048903 A185864 A115545
Adjacent sequences: A066878 A066879 A066880 * A066882 A066883 A066884
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KEYWORD
| nonn
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AUTHOR
| Jason Earls (zevi_35711(AT)yahoo.com), Jan 22 2002
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EXTENSIONS
| Terms a(16) etc. from R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Oct 01 2008
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