A124485 Numbers n such that 2n-1 and 4n-1 are primes.
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
Keywords
Links
- Muniru A Asiru, Table of n, a(n) for n = 1..5000
Crossrefs
Programs
-
GAP
Filtered([1..1000],p->IsPrime(2*p-1) and IsPrime(4*p-1)); # Muniru A Asiru, 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 *)
Formula
a(n) = (A005384(n+1) + 1)/2. - Hilko Koning, Jul 19 2018
Extensions
Extended by Ray Chandler, Nov 21 2006