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A007138
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Smallest primitive factor of 10^n -1. Also smallest prime p such that 1/p has repeating decimal expansion of period n.
(Formerly M2888)
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14
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3, 11, 37, 101, 41, 7, 239, 73, 333667, 9091, 21649, 9901, 53, 909091, 31, 17, 2071723, 19, 1111111111111111111, 3541, 43, 23, 11111111111111111111111, 99990001, 21401, 859, 757, 29, 3191, 211, 2791, 353, 67, 103, 71, 999999000001
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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REFERENCES
| J. Brillhart et al., Factorizations of b^n +- 1. Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 2nd edition, 1985; and later supplements.
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..500
J. Brillhart et al., Factorizations of b^n +- 1, Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 3rd edition, 2002.
S. S. Wagstaff, Jr., The Cunningham Project
Eric Weisstein's World of Mathematics, Decimal Expansion
Index entries for sequences related to decimal expansion of 1/n
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EXAMPLE
| a(3) = 37 since 1/37 = 0.027027... has period 3.
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CROSSREFS
| Cf. A046107.
Sequence in context: A069358 A108544 A095088 * A046107 A061075 A005422
Adjacent sequences: A007135 A007136 A007137 * A007139 A007140 A007141
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KEYWORD
| nonn
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com), Mira Bernstein, Robert G. Wilson v (rgwv(AT)rgwv.com), Jud McCranie
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