A032353 - OEIS

%I #34 Sep 08 2022 08:44:51

%S 2,4,6,14,20,26,50,52,92,120,174,180,190,290,320,390,432,616,830,1804,

%T 2256,6614,13496,15494,16696,22386,54486,88066,95330,207084,283034,

%U 561816,804534,811230,1491852,2139912,2167800,2915954,3015762,3511774,5775996

%N Numbers k such that 7*2^k+1 is prime.

%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 Y. Gallot, <a href="http://www.utm.edu/research/primes/programs/gallot/index.html">Proth.exe: Windows Program for Finding Large Primes</a>

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

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/ProthPrime.html">Proth Prime</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[10^3], PrimeQ[7*2^# + 1] &] (* _Michael De Vlieger_, Feb 25 2017 *)

%o (PARI) is(n)=ispseudoprime(7*2^n+1) \\ _Charles R Greathouse IV_, Feb 20 2017

%o (Magma) [n: n in [1..830] | IsPrime(7*2^n+1)]; // _Arkadiusz Wesolowski_, Feb 24 2017

%Y Cf. A002255, A050527.

%K nonn,hard

%O 1,1

%A _James R. Buddenhagen_

%E Added more terms (from http://web.archive.org/web/20161028080239/http://www.prothsearch.net/riesel.html), _Joerg Arndt_, Apr 07 2013

%E a(41) from _Jeppe Stig Nielsen_, Jul 25 2019