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

1,1

Links

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

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 *)

Crossrefs

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

Subsequence of A124493. Supersequence of A124017.

Sequence in context: A360966 A079038 A101790 * A075320 A071968 A170921

Adjacent sequences: A124491 A124492 A124493 * A124495 A124496 A124497

Keyword

nonn

Author

Artur Jasinski, Nov 04 2006

Extensions

Extended by Ray Chandler, Nov 22 2006

Status

approved