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A296446
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Numbers k such that 10^(2k)/2 + 10^k + 1 are prime.
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1
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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 10^(4k)+4.
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LINKS
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EXAMPLE
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61, 5101, 501001, 50010001, and 50000000010000000001 are prime, while 5000100001=13*1597*240841, 500001000001=2357*212134493, etc.
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MATHEMATICA
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ParallelMap[If[PrimeQ[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(10^(2*k)/2+10^k+1); \\ Michel Marcus, Dec 13 2017
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CROSSREFS
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See A296445 for 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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