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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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9
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1, 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; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| 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
| 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]
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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
| 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
| Cf. A058277, A006511.
Sequence in context: A024372 A061390 A051445 * A073692 A132012 A160690
Adjacent sequences: A002178 A002179 A002180 * A002182 A002183 A002184
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KEYWORD
| nonn
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
| Offset and initial term corrected Oct 07 2007
Revised definition from T. D. Noe, Aug 14 2008
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