A239741 - OEIS

%I #15 Sep 08 2022 08:46:07

%S 1,2,11,24,28,92,166,191,220,587,677,964,988,1840,2664,3604,6079,6640,

%T 8817,33647,34308,39882,44055,47050,64100,103313,223439,225921

%N Numbers k such that prime(k) * 2^k - 1 is prime.

%C The PFGW program has been used to certify all the terms up to a(28), using a deterministic test which exploits the factorization of a(n)+1.

%C a(29) > 290000.

%t Select[Range[1000], PrimeQ[Prime[#]*2^# - 1] &]

%o (Magma) [n: n in [0..1000] | IsPrime(NthPrime(n)*2^n-1)]; // _Vincenzo Librandi_, Dec 24 2015

%o (PARI) is(n,p=prime(n))=ispseudoprime(p<<n-1) \\ _Charles R Greathouse IV_, Jun 06 2017

%Y Cf. A239742.

%K nonn,more

%O 1,2

%A _Giovanni Resta_, Mar 26 2014