A196303 Numbers n such that both n and (n-1)*2^n+1 are primes.

2, 3, 7, 1471, 1483, 61627, 88731

Offset

1,1

Comments

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

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

Subsequence 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

Status

approved