cp's OEIS Frontend

A273009 Numbers k such that (2^k + 5) / 3 is prime.

%I A273009 #26 Oct 05 2024 13:22:41
%S A273009 0,2,4,6,12,18,24,42,84,300,390,780,822,2430,5508,5514,6492,12372,
%T A273009 22680,25770,169416,174240,383544,1007838,1572882
%N A273009 Numbers k such that (2^k + 5) / 3 is prime.
%C A273009 Larger members of the sequence generate probable primes only.
%C A273009 Corresponding prime numbers are: 2, 3, 7, 23, 1367, 87383, 5592407, 1466015503703,6447604371278022265099607,.. etc.
%H A273009 Henri & Renaud Lifchitz, <a href="http://www.primenumbers.net/prptop/searchform.php?form=%282%5En%2B5%29%2F3&amp;action=Search">(2^n+5)/3 PRPs</a> [PRP Top Records]
%F A273009 a(n) = 2*A261539(n).
%t A273009 Select[Range[0,10000], PrimeQ[(2^# + 5)/3] &]
%o A273009 (Magma) [n: n in [0..2000] | (2^n+5) mod 3 eq 0 and IsPrime((2^n+5) div 3)];
%o A273009 (PARI) is(n)=ispseudoprime((2^n+5)/3) \\ _Charles R Greathouse IV_, Jun 07 2016
%Y A273009 Cf. A261539.
%K A273009 nonn,more,hard
%O A273009 1,2
%A A273009 _Vincenzo Librandi_, May 13 2016