cp's OEIS Frontend

A142247 Primes of the form 2^p - 1, 2^p + 1, 2^p - 3, or 2^p + 3, where p is prime.

%I A142247 #6 Oct 01 2024 07:25:23
%S A142247 3,5,7,11,29,31,127,131,8191,131071,524287,536870909,2147483647,
%T A142247 2305843009213693951,147573952589676412931,
%U A142247 618970019642690137449562111,162259276829213363391578010288127
%N A142247 Primes of the form 2^p - 1, 2^p + 1, 2^p - 3, or 2^p + 3, where p is prime.
%F A142247 Union of A000668, A172041, and A057737. - _Jason Yuen_, Oct 01 2024
%t A142247 f[n_] := If[PrimeQ[2^Prime[n] - 1] || PrimeQ[2^Prime[n] + 1] || PrimeQ[2^Prime[n] - 3] || PrimeQ[2^Prime[n] + 3], {2^Prime[n] - 1, 2^Prime[n] + 1, 2^Prime[n] - 3, 2^Prime[n] + 3}, {}]; a = Flatten[Table[f[n], {n, 1, 100}]]; Union[Flatten[Table[If[PrimeQ[a[[n]]], a[[n]], {}], {n, 1, Length[a]}]]]
%Y A142247 Cf. A000668, A172041, A057737.
%K A142247 nonn,uned
%O A142247 1,1
%A A142247 _Roger L. Bagula_, Sep 18 2008