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 A050556 Numbers k such that 61*2^k-1 is prime. 0

%I

%S 3,5,9,13,17,19,25,39,63,67,75,119,147,225,419,715,895,1025,1103,1179,

%T 1345,1829,3855,4159,4493,6039,7799,9073,10543,12883,23807,23957,

%U 36163,44047,51975,65573,79393,79949,81987,86349,384287,499175,762417,971585

%N Numbers k such that 61*2^k-1 is prime.

%C 499175 is also a member. - Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008

%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 Kosmaj, <a href="http://www.15k.org/riesellist.html">Riesel list 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[61*2^# - 1] & ] (* _Robert Price_, Dec 22 2018 *)

%o (PARI) is(n)=ispseudoprime(61*2^n-1) \\ _Charles R Greathouse IV_, Jun 13 2017

%K hard,nonn,more

%O 1,1

%A _N. J. A. Sloane_, Dec 29 1999

%E More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008

%E a(42)-a(44) from the Wilfrid Keller link by _Robert Price_, Dec 22 2018

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Last modified July 20 14:01 EDT 2019. Contains 325181 sequences. (Running on oeis4.)