A059746 -id:A059746 - cp's OEIS frontend

A059747 Numbers k such that 3*2^k - 7 is prime.

2, 3, 4, 5, 8, 12, 15, 17, 20, 21, 45, 48, 87, 97, 113, 120, 172, 217, 228, 276, 312, 580, 692, 1132, 1588, 1668, 2576, 2591, 3780, 4311, 4412, 6205, 11952, 19897, 19941, 20525, 22821, 44757, 62833, 110437, 124113

Offset: 1

Robert G. Wilson v, Feb 10 2001

Next term > 12000. - Vincenzo Librandi, Sep 29 2012

Cf. A059746.

Do[ If[ PrimeQ[ 3*2^n - 7 ], Print[n] ], {n, 3000} ]
Select[Range[6500], PrimeQ[(3*2^# - 7)] &] (* Vincenzo Librandi, Sep 29 2012 *)

is(n)=ispseudoprime(3*2^n-7) \\ Charles R Greathouse IV, Jun 13 2017

a(29)-a(32) from Vincenzo Librandi, Sep 29 2012
a(33) from Bruno Berselli, Sep 30 2012
a(34)-a(39) from Michael S. Branicky, May 01 2023
a(40)-a(41) from Michael S. Branicky, Sep 27 2024

A227230 Numbers k such that 3*2^k + {5,7} are twin primes.

Original entry on oeis.org

1, 2, 3, 5, 6, 19, 22

Offset: 1

Zak Seidov, Sep 20 2013

No more terms up to 10^4.
Any subsequent terms exceed 200,000. - Lucas A. Brown, Sep 02 2024
Any subsequent terms exceed 10^6, by non-primality of 3*2^k+7 for members of b-file at A057913 > 22 and table in Section 6 of Grantham and Granville link. - Michael S. Branicky, Sep 07 2024

Jon Grantham and Andrew Granville, Fibonacci primes, primes of the form 2^n-k and beyond, arXiv:2307.07894 [math.NT], 2023.

Intersection of A057913 and A059746. - Jason Yuen, Sep 02 2024

Cf. A071558, A181490.

Reap[Do[If[PrimeQ[a=3*2^n+5]&&PrimeQ[a+2],Sow[n]],{n,150}]][[2,1]]

for(k = 1,10^4, if(ispseudoprime(a = 3*2^k + 5)&&ispseudoprime (a + 2), print1(k",")))

cp's OEIS Frontend

A059747 Numbers k such that 3*2^k - 7 is prime.

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