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A297421
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Numbers k such that (10^(2k) + 2*(10^k) + 4)/4 is prime.
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0
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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^(3k)-8.
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LINKS
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EXAMPLE
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31, 2551, 250501, and 250000000000000500000000000001 are prime, while 25005001=7*79*103*439, 2500050001=19*2269*57991, etc.
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MAPLE
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select(k->isprime((10^(2*k)+2*(10^k)+4)/4), [$1..1000]); # Muniru A Asiru, Apr 11 2018
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MATHEMATICA
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Select[Range[10^3], PrimeQ[(10^(2 #) + 2 (10^#) + 4)/4] &] (* Michael De Vlieger, Dec 30 2017 *)
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PROG
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(PARI) isok(k) = isprime((10^(2*k)+2*(10^k)+4)/4); \\ 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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