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

1, 3, 7, 237, 1885, 51381, 75765

Offset: 1

Author

Jason Earls, May 02 2001

Keywords

• hard
• nonn

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

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

Crossrefs

Cf. A061421.

Equals A100359(n) + 1.

Programs

PARI

is(n)=isprime(2^(n-1)+n) \\ Charles R Greathouse IV, May 22 2017

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