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Search: id:A005278
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| A005278 |
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Noncototients: n such that x-phi(x)=n has no solution.
(Formerly M4688)
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+0
20
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| 10, 26, 34, 50, 52, 58, 86, 100, 116, 122, 130, 134, 146, 154, 170, 172, 186, 202, 206, 218, 222, 232, 244, 260, 266, 268, 274, 290, 292, 298, 310, 326, 340, 344, 346, 362, 366, 372, 386, 394, 404, 412, 436, 466, 470, 474, 482, 490, 518, 520
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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If the strong Goldbach conjecture (every even number>6 is the sum of at least 2 distinct primes p and q) is true, sequence contains only even values. Since p*q-phi(p*q)=p+q-1 and then every odd number can be expressed as x-phi(x). - Benoit Cloitre (benoit7848c(AT)orange.fr), Mar 03 2002
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REFERENCES
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N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
J. Browkin and A. Schinzel, On integers not of the form n-phi(n), Colloq. Math., 68 (1995), 55-58. [Shows that this sequence is infinite. - Labos E. (labos(AT)ana.sote.hu), Dec 21 1999]
R. K. Guy, Unsolved Problems in Number Theory, B36.
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LINKS
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T. D. Noe, Table of n, a(n) for n=1..963
Eric Weisstein's World of Mathematics, Link to a section of The World of Mathematics.
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CROSSREFS
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Cf. A006093, A126887. Complement of A051953.
Sequence in context: A043342 A023715 A045143 this_sequence A157075 A045039 A080059
Adjacent sequences: A005275 A005276 A005277 this_sequence A005279 A005280 A005281
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KEYWORD
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nonn,nice
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
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More terms from Jud McCranie (j.mccranie(AT)comcast.net) 1/97.
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