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A051948
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Numbers n such that n*sigma(n) == 2 mod phi(n).
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1
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2, 3, 4, 5, 6, 7, 11, 13, 17, 19, 22, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 241
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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REFERENCES
| R. K. Guy, Unsolved Problems Number Theory, B37.
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LINKS
| Chris Nash, There no other solutions besides 4, 6, 22 and the primes (html, pdf) [?Broken link]
C. Rivera, Puzzle 76
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PROG
| (PARI) a(n)=if(n<12, [2, 3, 4, 5, 6, 7, 11, 13, 17, 19, 22][n], prime(n-3)) \\ Charles R Greathouse IV, Aug 26 2011
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CROSSREFS
| Cf. A002270.
Sequence in context: A090563 A045745 A054010 * A193461 A192587 A174323
Adjacent sequences: A051945 A051946 A051947 * A051949 A051950 A051951
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KEYWORD
| nonn,nice,easy
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com), Dec 21 1999
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