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A124485
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Numbers n such that 2n-1 and 4n-1 are primes.
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17
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2, 3, 6, 12, 15, 21, 27, 42, 45, 57, 66, 87, 90, 96, 117, 120, 126, 141, 147, 180, 210, 216, 222, 246, 255, 297, 321, 327, 330, 342, 360, 372, 381, 405, 456, 477, 507, 510, 516, 525, 552, 612, 615, 645, 705, 720, 726, 741, 750, 756, 780, 792, 801, 867, 906, 945
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OFFSET
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1,1
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LINKS
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FORMULA
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MAPLE
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select(k->isprime(2*k-1) and isprime(4*k-1), [$1..1000]); # Muniru A Asiru, Jul 19 2018
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MATHEMATICA
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Select[Range[1000], And @@ PrimeQ /@ ({2, 4}*# - 1) &] (* Ray Chandler, Nov 21 2006 *)
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PROG
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(GAP) Filtered([1..1000], p->IsPrime(2*p-1) and IsPrime(4*p-1)); # Muniru A Asiru, Jul 19 2018
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CROSSREFS
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Cf. A005384 (Sophie Germain primes).
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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