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A156983 Primes of the form 2^k + 21. 1
23, 29, 37, 53, 149, 277, 2069, 32789, 65557, 524309, 17592186044437, 281474976710677, 2251799813685269, 4503599627370517, 2305843009213693973, 11692013098647223345629478661730264157247460343829 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..16.

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. A019434 (2^(2^n)+1), A057733 (2^n+3), A123250 (2^n+5).

Sequence in context: A180066 A101784 A101802 * A230456 A174196 A144226

Adjacent sequences:  A156980 A156981 A156982 * A156984 A156985 A156986

KEYWORD

nonn

AUTHOR

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

EXTENSIONS

More terms from Vincenzo Librandi, Apr 29 2010

STATUS

approved

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Last modified August 7 22:40 EDT 2020. Contains 336279 sequences. (Running on oeis4.)