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A128461
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Numbers k such that 21^k - 2 is a prime.
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12
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1, 2, 4, 10, 21, 25, 27, 32, 60, 88, 106, 120, 146, 264, 828, 965, 1944, 4822, 12089, 14427, 17354, 42335, 46395, 58348, 190632
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OFFSET
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1,2
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COMMENTS
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LINKS
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MATHEMATICA
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Do[ f = 21^n - 2; If[ PrimeQ[ f ], Print[ {n, f} ] ], {n, 1, 1000} ]
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CROSSREFS
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Cf. A084714 (smallest prime of the form (2n-1)^k - 2).
Cf. A128472 (smallest prime of the form (2n-1)^k - 2 for k > (2n-1)).
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KEYWORD
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nonn,hard,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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