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A124485 Numbers n such that 2n-1 and 4n-1 are primes. 17
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 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
FORMULA
a(n) = (A005384(n+1) + 1)/2. - Hilko Koning, Jul 19 2018
MAPLE
select(k->isprime(2*k-1) and isprime(4*k-1), [$1..1000]); # Muniru A Asiru, Jul 19 2018
MATHEMATICA
Select[Range[1000], And @@ PrimeQ /@ ({2, 4}*# - 1) &] (* Ray Chandler, Nov 21 2006 *)
PROG
(GAP) Filtered([1..1000], p->IsPrime(2*p-1) and IsPrime(4*p-1)); # Muniru A Asiru, Jul 19 2018
CROSSREFS
Cf. A005384 (Sophie Germain primes).
Sequence in context: A217647 A070926 A226023 * A200175 A286906 A125867
KEYWORD
nonn
AUTHOR
Artur Jasinski, Nov 04 2006
EXTENSIONS
Extended by Ray Chandler, Nov 21 2006
STATUS
approved

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Last modified April 22 01:34 EDT 2024. Contains 371887 sequences. (Running on oeis4.)