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A007015
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a(n) = smallest k such that phi(n+k) = phi(k).
(Formerly M3212)
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4
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1, 4, 3, 8, 5, 24, 5, 13, 9, 20, 7, 48, 13, 16, 13, 26, 17, 52, 19, 37, 21, 44, 13, 96, 25, 34, 27, 32, 13, 124, 17, 52, 33, 41, 19, 104, 35, 52, 37, 65, 25, 123, 17, 73, 39, 92, 41, 183, 35, 76, 39, 68, 53, 156, 35, 64, 57, 116, 41, 248, 61, 73, 61, 104, 65, 144, 67, 82
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Sierpinski proved that a solution exists for each n>0.
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REFERENCES
| M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards Applied Math. Series 55, 1964 (and various reprintings), p. 840.
R. K. Guy, Unsolved Problems Number Theory, Sect. B36
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
| T. D. Noe, Table of n, a(n) for n=1..10000
M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards, Applied Math. Series 55, Tenth Printing, 1972 [alternative scanned copy].
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MATHEMATICA
| kphi[n_]:=Module[{k=1}, While[EulerPhi[n+k]!=EulerPhi[k], k++]; k]; Array[kphi, 70] (* From Harvey P. Dale, Oct 24 2011 *)
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PROG
| (Haskell)
import Data.List (elemIndex)
import Data.Maybe (fromJust)
a007015 n = 1 + (fromJust $
elemIndex 0 $ zipWith (-) a000010_list $ drop n a000010_list)
-- Reinhard Zumkeller, Feb 10 2012
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CROSSREFS
| Cf. A000010.
Sequence in context: A082895 A086938 A126084 * A114562 A189042 A011451
Adjacent sequences: A007012 A007013 A007014 * A007016 A007017 A007018
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KEYWORD
| nonn,nice,changed
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com), Mira Bernstein, Robert G. Wilson v (rgwv(AT)rgwv.com)
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EXTENSIONS
| More terms from Jud McCranie (JudMcCranie(AT)ugaalum.uga.edu), Dec 24 1999
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