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A297422
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Numbers k such that 4*10^(2k) + 2*(10^k) + 1 is prime.
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2
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0, 1, 3, 5, 10, 196, 251, 310, 415, 1107, 2422
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OFFSET
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1,3
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COMMENTS
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Numbers of this form divide 8*(10^3k)-1.
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LINKS
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EXAMPLE
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7, 421, 4002001, and 40000200001 are prime, while 40201=7*5743, 400020001=31*12903871, etc.
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MAPLE
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select(k->isprime(4*10^(2*k)+2*(10^k)+1), [$0..1000]); # Muniru A Asiru, Apr 11 2018
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MATHEMATICA
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Select[Range[1500], PrimeQ[4 (10^(2 #)) + 2 (10^#) + 1] &] (* Michael De Vlieger, Dec 30 2017 *)
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PROG
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(PARI) isok(k) = isprime(4*10^(2*k)+2*(10^k)+1); \\ Michel Marcus, Dec 30 2017
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CROSSREFS
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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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