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A059622 Numbers k such that (5*3^k - 7)/2 is prime. 1
2, 4, 16, 24, 32, 40, 120, 124, 144, 172, 186, 376, 700, 1232, 1264, 2894, 5054, 14826, 16498, 18348 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

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

LINKS

Table of n, a(n) for n=1..20.

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

STATUS

approved

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Last modified August 4 03:57 EDT 2021. Contains 346442 sequences. (Running on oeis4.)