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Search: id:A002181
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| A002181 |
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Least number k such that phi(k) = n, where n runs through the values (A002202) taken by phi.
(Formerly M2421 N0957)
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+0
8
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| 0, 3, 5, 7, 15, 11, 13, 17, 19, 25, 23, 35, 29, 31, 51, 37, 41, 43, 69, 47, 65, 53, 81, 87, 59, 61, 85, 67, 71, 73, 79, 123, 83, 129, 89, 141, 97, 101, 103, 159, 107, 109, 121, 113, 177, 143, 127, 255, 131, 161, 137, 139, 213, 185, 149, 151, 157, 187, 163, 249, 167, 203, 173
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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Inverse of Euler totient function.
A051445 without the zeros. The values of n are in A002180.
According to Guy, the first even term is for 2n=16842752=257*2^16. If there are only five Fermat primes, then terms will be even for 2n=2^r for all r>31. This was discussed in problem E3361. [From T. D. Noe (noe(AT)sspectra.com), Aug 14 2008]
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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).
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
J. W. L. Glaisher, Number-Divisor Tables. British Assoc. Math. Tables, Vol. 8, Camb. Univ. Press, 1940, p. 64.
R. K. Guy, Unsolved problems in number theory, B39. [From T. D. Noe (noe(AT)sspectra.com), Aug 14 2008]
William P. Wardlaw, L. L. Foster and R. J. Simpson, Problem E3361, Amer. Math. Monthly, Vol. 98, No. 5 (May, 1991), 443-444. [From T. D. Noe (noe(AT)sspectra.com), Aug 14 2008]
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LINKS
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T. D. Noe, Table of n, a(n) for n=1..10000
T. D. Noe, Numbers Like 16842752 [From T. D. Noe (noe(AT)sspectra.com), Aug 19 2008]
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CROSSREFS
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Cf. A058277, A006511.
Adjacent sequences: A002178 A002179 A002180 this_sequence A002182 A002183 A002184
Sequence in context: A024372 A061390 A051445 this_sequence A073692 A132012 A160690
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KEYWORD
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nonn
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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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Offset and initial term corrected Oct 07 2007
Revised definition from T. D. Noe, Aug 14 2008
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