A196303 Primes p such that (p-1)*2^p+1 is also prime.
2, 3, 7, 1471, 1483, 61627, 88651
Offset: 1
Keywords
Examples
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.
Programs
-
Mathematica
Select[Prime[Range[9000]],PrimeQ[(#-1)2^#+1]&] (* Harvey P. Dale, Jan 19 2012 *)
-
PARI
forprime(n=1,1e4,if(ispseudoprime((n-1)<
Extensions
a(7) corrected by Michael S. Branicky, May 14 2025
Comments