Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #13 Sep 08 2022 08:46:15
%S 3,4,6,94
%N Numbers n such that 2^n - 3 and 3*2^n - 1 are both prime.
%C The intersection of A002235 and A050414 is not empty (3 does not belong to A267985).
%F A002235 INTERSECT A050414.
%e a(3) = 6 because 2^6 - 3 = 61 and 3*2^6 - 1 = 191 are both prime.
%o (Magma) [n: n in [2..94] | IsPrime(2^n-3) and IsPrime(3*2^n-1)];
%o (PARI) isok(n) = isprime(2^n-3) && isprime(3*2^n-1);
%Y Cf. A002235, A007505, A050414, A050415, A238694, A267985.
%K nonn,hard,more
%O 1,1
%A _Arkadiusz Wesolowski_, Jan 22 2016