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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
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 * A373084 A200175 A286906
KEYWORD
nonn
AUTHOR
Artur Jasinski, Nov 04 2006
EXTENSIONS
Extended by Ray Chandler, Nov 21 2006
STATUS
approved