A061422 Numbers k such that 2^(k-1) + k is prime.

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.

Links

Table of n, a(n) for n=1..7.

K. S. Brown, The Sum of the Prime Factors of N. MathPages.com

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: A349838 A179859 A377653 * A206333 A088097 A064774

Adjacent sequences: A061419 A061420 A061421 * A061423 A061424 A061425

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