A196303 Primes p such that (p-1)*2^p+1 is also prime.

2, 3, 7, 1471, 1483, 61627, 88651

Offset

1,1

Links

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

Example

a(1) = 2 because 2 and (2-1)*2^2 + 1 = 5 are both prime.
a(2) = 3 because 3 and (3-1)*2^3 + 1 = 17 are both prime.
a(3) = 7 because 7 and (7-1)*2^7 + 1 = 769 are both prime.

Mathematica

Select[Prime[Range[9000]], PrimeQ[(#-1)2^#+1]&] (* Harvey P. Dale, Jan 19 2012 *)

Prog

(PARI) forprime(n=1, 1e4, if(ispseudoprime((n-1)<<n+1), print1(n", "))) \\ Charles R Greathouse IV, Oct 09 2011

Crossrefs

Prime terms of A128001.

Cf. A029544, A196421, A196446.

Sequence in context: A266276 A088252 A334021 * A048979 A201363 A088332

Adjacent sequences: A196300 A196301 A196302 * A196304 A196305 A196306

Keyword

nonn

Author

Juri-Stepan Gerasimov, Oct 02 2011

Extensions

a(7) corrected by Michael S. Branicky, May 14 2025

Status

approved