This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A179658 #24 Aug 28 2025 06:52:25
%S A179658 3,1,3,15,45,3,99,45,51,141,153,177,411,45,45,267,237,75,75,207,111,
%T A179658 111,123,159,57,375,1419,45,291,321,489,585,525,1623,579,45,27,1293,
%U A179658 1059,255,2265,33,465,165,405,315,315,117,411,1725,2343,2397,465,315,1443
%N A179658 Minimal odd k such that k*2^n-1 and k*2^(n+1)-1 are Sophie Germain primes.
%C A179658 In the b-file up to n=10000, only a(2) is not a multiple of 3 and all entries are odd, so heuristically a(n) = A176248(n) for n>2. - _R. J. Mathar_, Aug 28 2025
%H A179658 Amiram Eldar, <a href="/A179658/b179658.txt">Table of n, a(n) for n = 1..10000</a> (from Bonath's link)
%H A179658 Karsten Bonath, <a href="http://www.rieselprime.de/Related/FirstSG.htm">First odd k for which k * 2^n - 1 and k * 2^(n + 1) - 1 are prime</a>.
%e A179658 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.
%t A179658 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 *)
%o A179658 (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
%Y A179658 Cf. A005384, A076806 (minimal odd k such that k*2^n-1 and k*2^n+1 are twin primes).
%K A179658 nonn,changed
%O A179658 1,1
%A A179658 _Karsten Bonath_, Jul 23 2010
%E A179658 More terms from Bonath's link added by _Amiram Eldar_, Jan 16 2020