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A056716
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Numbers n such that 6*10^n-1 is prime.
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4
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0, 1, 2, 4, 5, 7, 10, 13, 22, 23, 28, 34, 40, 61, 73, 361, 490, 613, 1624, 2000, 2994, 4301, 4332, 18668, 32544, 34936, 267598, 270658, 293134, 319889, 414508
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OFFSET
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1,3
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COMMENTS
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Also numbers n such that 5*10^n + 9*R_n is prime, where R_n = 11...1 is the repunit (A002275) of length n.
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LINKS
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MATHEMATICA
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Do[ If[ PrimeQ[ 6*10^n - 1], Print[n]], {n, 0, 5000}]
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PROG
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CROSSREFS
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KEYWORD
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hard,nonn,more
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AUTHOR
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EXTENSIONS
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3 more terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Dec 30 2007
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STATUS
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approved
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