A124494 Numbers k for which 2*k-1, 4*k-1, 8*k-1 and 16*k-1 are primes.

3, 45, 90, 180, 255, 615, 705, 1350, 1770, 3225, 5295, 5775, 5955, 6060, 8580, 9855, 9945, 11175, 13095, 13740, 15195, 21825, 26820, 26925, 27615, 28920, 30075, 30705, 31710, 33375, 35700, 37350, 37665, 41250, 43770, 49185, 50700, 52185, 53640

Offset: 1

Author

Artur Jasinski, Nov 04 2006

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A006254, A124485, A125113, A124514, A124515, A124516.

Subsequence of A124493. Supersequence of A124017.

Programs

Mathematica

Select[3*Range[20000], And @@ PrimeQ /@ ({2, 4, 8, 16}*# - 1) &] (* Ray Chandler, Nov 22 2006 *)
Select[Range[3,55000,3],AllTrue[2^Range[4] #-1,PrimeQ]&] (* or, faster  *) Join[{3},Select[Range[ 15,55000,15],AllTrue[ 2^Range[4] #-1,PrimeQ]&]] (* Harvey P. Dale, Feb 02 2025 *)

Extensions

Extended by Ray Chandler, Nov 22 2006