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A179658
Minimal odd k such that k*2^n-1 and k*2^(n+1)-1 are Sophie Germain primes.
1
3, 1, 3, 15, 45, 3, 99, 45, 51, 141, 153, 177, 411, 45, 45, 267, 237, 75, 75, 207, 111, 111, 123, 159, 57, 375, 1419, 45, 291, 321, 489, 585, 525, 1623, 579, 45, 27, 1293, 1059, 255, 2265, 33, 465, 165, 405, 315, 315, 117, 411, 1725, 2343, 2397, 465, 315, 1443
OFFSET
1,1
EXAMPLE
Example for n=7: a(7)=99 because 99*2^7-1 and 99*2^8-1 is the first occurrence for n=7 as a Sophie Germain prime pair.
MATHEMATICA
a[n_] := Module[{k = 1}, While[!And @@ PrimeQ[k * 2^{n, n+1} - 1], k += 2]; k]; Array[a, 30] (* Amiram Eldar, Jan 16 2020 *)
PROG
(Magma) a:=[]; for n in [1..55] do k:=1; while not (IsPrime(k*2^n-1) and IsPrime(k*2^(n+1)-1)) do k:=k+2; end while; Append(~a, k); end for; a; // Marius A. Burtea, Jan 16 2020
CROSSREFS
Cf. A005384, A076806 (minimal odd k such that k*2^n-1 and k*2^n+1 are twin primes).
Sequence in context: A355793 A173424 A143081 * A112811 A197272 A306773
KEYWORD
nonn
AUTHOR
Karsten Bonath, Jul 23 2010
EXTENSIONS
More terms from Bonath's link added by Amiram Eldar, Jan 16 2020
STATUS
approved