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A093177
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Primes of the form 90*R_n + 1, where R_n is the repunit (A002275) of length n.
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9
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991, 99991, 9999991, 999999999999999999999999999999991, 999999999999999999999999999999999999999999991, 999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999991
(list;
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listen;
history;
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OFFSET
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1,1
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COMMENTS
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Primes of the form 10^n-9 (n=3,5,7,..,) [From Vincenzo Librandi, Nov 16 2010]
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LINKS
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Table of n, a(n) for n=1..6.
Makoto Kamada, Prime numbers of the form 99...991
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FORMULA
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a(n) = 10^(A056696(n)+1) - 9 = 10^A095714(n) - 9.
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CROSSREFS
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Cf. A056696 (corresponding n), A095714.
Sequence in context: A031790 A137703 A155509 * A161926 A172698 A109149
Adjacent sequences: A093174 A093175 A093176 * A093178 A093179 A093180
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KEYWORD
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nonn
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AUTHOR
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Rick L. Shepherd, Mar 27 2004
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EXTENSIONS
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Edited by Ray Chandler, Feb 26 2012
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STATUS
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approved
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