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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

Muniru A Asiru, Table of n, a(n) for n = 1..5000

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).

Cf. A124486, A124487, A124488, A124489, A124490, A124491, A124492.

Sequence in context: A217647 A070926 A226023 * A200175 A286906 A125867

Adjacent sequences:  A124482 A124483 A124484 * A124486 A124487 A124488

KEYWORD

nonn

AUTHOR

Artur Jasinski, Nov 04 2006

EXTENSIONS

Extended by Ray Chandler, Nov 21 2006

STATUS

approved

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Last modified September 20 21:08 EDT 2019. Contains 327247 sequences. (Running on oeis4.)