A059622 Numbers k such that (5*3^k - 7)/2 is prime.

2, 4, 16, 24, 32, 40, 120, 124, 144, 172, 186, 376, 700, 1232, 1264, 2894, 5054, 14826, 16498, 18348, 33416

Offset

1,1

Comments

a(21) > 20000. - Jinyuan Wang, Jan 28 2020

Links

Table of n, a(n) for n=1..21.

Mathematica

Do[ If[ PrimeQ[ (5*3^n - 7)/2 ], Print[n] ], {n, 0, 10000} ]
Select[Range[5100], PrimeQ[(5*3^#-7)/2]&] (* Harvey P. Dale, Jul 15 2018 *)

Prog

(PARI) is(n)=ispseudoprime((5*3^n-7)/2) \\ Charles R Greathouse IV, Jun 13 2017
(Magma) [k: k in [0..1000] | IsPrime((5*3^k - 7) div 2)]; // Jinyuan Wang, Jan 28 2020

Crossrefs

Cf. A059621 ((5*3^k+7)/2 is prime).

Sequence in context: A193868 A256788 A324211 * A131475 A239363 A045541

Adjacent sequences: A059619 A059620 A059621 * A059623 A059624 A059625

Keyword

nonn,more

Author

Robert G. Wilson v, Feb 19 2001

Extensions

a(18)-a(20) from Jinyuan Wang, Jan 28 2020

a(21) from Michael S. Branicky, Apr 29 2023

Status

approved