

A124485


Numbers n such that 2n1 and 4n1 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*k1) and isprime(4*k1), [$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*p1) and IsPrime(4*p1)); # 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



