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A059242
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Numbers k such that 2^k + 5 is prime.
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26
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1, 3, 5, 11, 47, 53, 141, 143, 191, 273, 341, 16541, 34001, 34763, 42167, 193965, 282203
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OFFSET
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1,2
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COMMENTS
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The subsequence of primes starts 3, 5, 11, 47, 53, 191, ... - Vincenzo Librandi, Aug 07 2010
For k in this sequence, 2^(k-1)*(2^k+5) is in A141548: numbers of deficiency 6. - M. F. Hasler, Apr 23 2015
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LINKS
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Henri Lifchitz and Renaud Lifchitz (Editors), Search for 2^n+5, PRP Top Records.
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EXAMPLE
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2^3 + 5 = 13 is prime, but 2^4 + 5 = 21 is not.
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MATHEMATICA
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PROG
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(PARI) is(n)=ispseudoprime(2^n+5) \\ M. F. Hasler, Apr 23 2015
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CROSSREFS
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Cf. A019434 (primes 2^k+1), A057732 (2^k+3), this sequence (2^k+5), A057195 (2^k+7), A057196 (2^k+9), A102633 (2^k+11), A102634 (2^k+13), A057197 (2^k+15), A057200 (2^k+17), A057221 (2^k+19), A057201 (2^k+21), A057203 (2^k+23).
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KEYWORD
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nonn,hard,more
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AUTHOR
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Tony Davie (ad(AT)dcs.st-and.ac.uk), Jan 21 2001
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EXTENSIONS
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More terms from Santi Spadaro, Oct 04 2002
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STATUS
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approved
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