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A156983 Primes of the form 2^k + 21. 2

%I #20 Nov 08 2023 12:09:21

%S 23,29,37,53,149,277,2069,32789,65557,524309,17592186044437,

%T 281474976710677,2251799813685269,4503599627370517,

%U 2305843009213693973,11692013098647223345629478661730264157247460343829

%N Primes of the form 2^k + 21.

%F a(n) = 2^A057201(n) + 21. - _Elmo R. Oliveira_, Nov 08 2023

%e 23 = 2^1 + 21 is in the sequence; 29 = 2^3 + 21 is in the sequence.

%t Delete[Union[Table[If[PrimeQ[2^n + 21], 2^n + 21, 0], {n, 1, 500}]],1]

%o (Magma) [ a: n in [1..200] | IsPrime(a) where a is 2^n+21 ]; // _Vincenzo Librandi_, Nov 27 2010

%Y Cf. A000040, A019434 (2^(2^k) + 1), A057201, A057733 (2^k + 3), A123250 (2^k + 5).

%K nonn

%O 1,1

%A Edwin Dyke (ed.dyke(AT)btinternet.com), Feb 20 2009

%E More terms from _Vincenzo Librandi_, Apr 29 2010

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Last modified March 28 09:04 EDT 2024. Contains 371240 sequences. (Running on oeis4.)