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A061422
Numbers k such that 2^(k-1) + k is prime.
4
1, 3, 7, 237, 1885, 51381, 75765
OFFSET
1,2
COMMENTS
No other terms below 300000. - Giovanni Resta, Nov 12 2012
a(8) > 500000. - Robert Price, May 24 2014
REFERENCES
J.-M. De Koninck, Ces nombres qui nous fascinent, Entry 237, p. 66, Ellipses, Paris 2008.
PROG
(PARI) is(n)=isprime(2^(n-1)+n) \\ Charles R Greathouse IV, May 22 2017
CROSSREFS
Cf. A061421.
Equals A100359(n) + 1.
Sequence in context: A349006 A349838 A179859 * A206333 A088097 A064774
KEYWORD
hard,nonn
AUTHOR
Jason Earls, May 02 2001
EXTENSIONS
H. Zeisel found the probable prime 1885. - Benoit Cloitre, Jun 03 2002
New term 51381 from Nuutti Kuosa (see MathPages link). - Max Alekseyev, Feb 08 2009
Deleted an incorrect conjecture. - N. J. A. Sloane, Dec 27 2009
a(7) from Giovanni Resta, Nov 12 2012
STATUS
approved