login
Numbers k such that 231*2^k+1 is prime.
1

%I #32 Dec 21 2024 04:11:42

%S 1,4,5,7,9,11,12,13,15,27,33,65,85,89,105,120,149,161,175,229,279,295,

%T 307,355,453,528,625,697,807,831,879,901,935,988,1265,1432,1645,1761,

%U 1899,1939,2497,3101,5176,5181,9809,14025,21765,27333,35271,36717,40935

%N Numbers k such that 231*2^k+1 is prime.

%H Jeppe Stig Nielsen, <a href="/A032492/b032492.txt">Table of n, a(n) for n = 1..79</a> (terms n = 1..72 from Robert Price)

%H Ray Ballinger, <a href="http://www.prothsearch.com/index.html">Proth Search Page</a>

%H Ray Ballinger and Wilfrid Keller, <a href="http://www.prothsearch.com/riesel1.html">List of primes k.2^n + 1 for k < 300</a>

%H Wilfrid Keller, <a href="http://www.prothsearch.com/riesel2.html">List of primes k.2^n - 1 for k < 300</a>

%H <a href="/index/Pri#riesel">Index entries for sequences of n such that k*2^n-1 (or k*2^n+1) is prime</a>

%t Select[Range[1000], PrimeQ[231*2^# + 1] & ] (* _Robert Price_, Dec 19 2018 *)

%o (PARI) is(n)=ispseudoprime(231*2^n+1) \\ _Charles R Greathouse IV_, Jun 13 2017

%K nonn,hard

%O 1,2

%A _N. J. A. Sloane_.

%E a(51)-a(72) from the Ray Ballinger and Wilfrid Keller link by _Robert Price_, Dec 19 2018