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A296443
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Numbers k such that 2*10^(2k)-2*10^k+1 is prime.
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1
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1, 2, 6, 7, 8, 315, 667, 5125, 7301, 10500, 11096
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OFFSET
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1,2
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COMMENTS
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Numbers of this form divide 4*10^(4k)+1.
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LINKS
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EXAMPLE
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181, 19801, 1999998000001, 199999980000001, and 19999999800000001 are prime, while 1998001=277*7213, 199980001=13*41*457*821, and 19999800001=53*5953*63389.
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MATHEMATICA
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ParallelMap[If[PrimeQ[2*10^(2 #) - 2*10^# + 1], #, Nothing] &, Range@ 4000] (* Robert G. Wilson v, Dec 13 2017 *)
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PROG
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(PARI) isok(k) = isprime(2*10^(2*k)-2*10^k+1); \\ Michel Marcus, Dec 13 2017
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CROSSREFS
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See A296444 for 2*10^(2k)+2*10^k+1.
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KEYWORD
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nonn,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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