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A084738
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Smallest prime of the form (n^k-1)/(n-1), or 0 if no such prime exists.
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7
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3, 13, 5, 31, 7, 2801, 73, 0, 11, 50544702849929377, 13, 30941, 211, 241, 17, 307, 19, 109912203092239643840221, 421, 463, 23, 292561, 601, 0, 321272407, 757, 29, 732541, 31, 917087137, 0, 1123, 2458736461986831391
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OFFSET
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2,1
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COMMENTS
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As mentioned by Dubner, when n is a power (greater than 1) of a prime, then (n^k-1)/(n-1) will usually be composite for all k, which is the case for n = 9, 25, 32 and 49. - T. D. Noe, Jan 23 2004
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LINKS
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Table of n, a(n) for n=2..34.
H. Dubner, Generalized repunit primes, Math. Comp., 61 (1993), 927-930.
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EXAMPLE
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a(8) = 73 = (8^3-1)/(8-1).
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MATHEMATICA
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Table[SelectFirst[(n^# - 1)/(n - 1) & /@ Range[10^3], PrimeQ] /. k_ /; MissingQ@ k -> 0, {n, 2, 34}] (* Michael De Vlieger, Apr 24 2017, Version 10.2 *)
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CROSSREFS
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Cf. A076481.
Cf. A084740 (least k such that (n^k-1)/(n-1) is prime).
Sequence in context: A187023 A331806 A331807 * A073580 A340349 A326609
Adjacent sequences: A084735 A084736 A084737 * A084739 A084740 A084741
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KEYWORD
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nonn
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AUTHOR
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Amarnath Murthy and Meenakshi Srikanth (menakan_s(AT)yahoo.com), Jun 15 2003
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EXTENSIONS
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More terms from T. D. Noe, Jan 23 2004
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STATUS
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approved
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