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%I #15 Nov 28 2023 17:53:51
%S 1,2,4,5,7,8,20,22,43,55,67,77,92,97,154,160,533,748,1432,3143,6427,
%T 8257,8270,9623,12269,28822,32683,42638,97427,133340,188395,239044
%N Numbers k such that 4^k + 27 is prime.
%C The next terms are > 239044.
%C Contains exactly the halved even terms of A157007.
%e For k = 22, 4^22 + 27 = 17592186044443 is prime.
%t Select[Range[0, 250000], PrimeQ[4^# + 27] &]
%o (Magma) [n: n in [0..700] | IsPrime(4^n+27)]; // _Vincenzo Librandi_, Oct 06 2015
%o (PARI) for(n=1, 1e3, if(isprime(4^n+3^3), print1(n", "))) \\ _Altug Alkan_, Oct 06 2015
%Y Cf. A157007, A253772 (similar sequence).
%K nonn,more
%O 1,2
%A _Robert Price_, Oct 05 2015
%E a(32) derived from A157007 by _Elmo R. Oliveira_, Nov 28 2023