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A156983
Primes of the form 2^k + 21.
2
23, 29, 37, 53, 149, 277, 2069, 32789, 65557, 524309, 17592186044437, 281474976710677, 2251799813685269, 4503599627370517, 2305843009213693973, 11692013098647223345629478661730264157247460343829
OFFSET
1,1
FORMULA
a(n) = 2^A057201(n) + 21. - Elmo R. Oliveira, Nov 08 2023
EXAMPLE
23 = 2^1 + 21 is in the sequence; 29 = 2^3 + 21 is in the sequence.
MATHEMATICA
Delete[Union[Table[If[PrimeQ[2^n + 21], 2^n + 21, 0], {n, 1, 500}]], 1]
PROG
(Magma) [ a: n in [1..200] | IsPrime(a) where a is 2^n+21 ]; // Vincenzo Librandi, Nov 27 2010
CROSSREFS
Cf. A000040, A019434 (2^(2^k) + 1), A057201, A057733 (2^k + 3), A123250 (2^k + 5).
Sequence in context: A101784 A101802 A363074 * A230456 A174196 A144226
KEYWORD
nonn
AUTHOR
Edwin Dyke (ed.dyke(AT)btinternet.com), Feb 20 2009
EXTENSIONS
More terms from Vincenzo Librandi, Apr 29 2010
STATUS
approved