|
%I #30 Aug 01 2019 18:39:56
%S 0,1,2,7,18,55,69,87,119,141,189,249,354,1586,2135,2865,2930,4214,
%T 7167,67485,74402,79326
%N Numbers k such that 6*7^k - 1 is prime.
%C a(23) > 2*10^5. - _Robert Price_, Nov 13 2015
%D R. K. Guy, Unsolved Problems in Number Theory, Section A3.
%H H. C. Williams, <a href="http://matwbn.icm.edu.pl/ksiazki/aa/aa39/aa3912.pdf">The primality of certain integers of the form 2Ar^n - 1</a>, Acta Arith. 39 (1981), 7-17.
%t Do[ If[ PrimeQ[6*7^n - 1], Print[n]], {n, 0, 5650}]
%o (PARI) for(n=0,2000, if(isprime(6*7^n-1),print1(n, ", ")))
%Y Cf. A003307, A002235, A046865, A079906, A001771, A005541, A056725, A046867, A079907.
%K nonn,hard,more
%O 1,3
%A _N. J. A. Sloane_
%E One more term from _Jason Earls_, Jul 21 2001
%E More terms from _Robert G. Wilson v_, Jan 17 2003
%E One more term from _Ryan Propper_, Jun 05 2006
%E a(20)-a(22) from _Donovan Johnson_, Nov 26 2008
%E First term 0 inserted by _Georg Fischer_, Aug 01 2019
|
