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A140790
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Numbers n such that phi(n)*sigma(n)=phi(n-1)*sigma(n-1) (phi is the Euler totient function A000010 and sigma is the sum-of-divisors function A000203).
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6, 56, 57, 124, 136, 148, 176, 305, 352, 645, 1016, 2465, 19305, 19305, 61132, 162525, 476672, 567645, 712725, 801945, 2435489, 3346400, 3885057, 4556000, 8085561, 8369361, 12516693, 22702120, 29628801, 83884032, 83994625, 84789248, 354812536, 860616296
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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REFERENCES
| J.-M. De Koninck, Ces nombres qui nous fascinent, Entry 136, pp 46, Ellipses, Paris 2008.
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LINKS
| K. Matthews, Factorizing n and calculating phi(n),omega(n),d(n),sigma(n) and mu(n)
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EXAMPLE
| 124 is in the sequence because phi(124)*sigma(124)=60*224=13440 and phi(123)*sigma(123)=80*168=13440,so that we indeed have phi(124)*sigma(124)=phi(123)*sigma(123).
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CROSSREFS
| Sequence in context: A095652 A132689 A183594 * A137033 A045526 A164579
Adjacent sequences: A140787 A140788 A140789 * A140791 A140792 A140793
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KEYWORD
| nonn
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AUTHOR
| Lekraj Beedassy (blekraj(AT)yahoo.com), Jul 14 2008
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EXTENSIONS
| a(30)-a(34) from Donovan Johnson (donovan.johnson(AT)yahoo.com), Jul 25 2011
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