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A057018
Numbers k such that (10*7^k -1)/3 is prime.
0
0, 1, 2, 14, 29, 38, 40, 59, 62, 64, 76, 80, 101, 491, 1024, 1814, 1826, 13733, 50516
OFFSET
1,3
COMMENTS
No further terms through k = 5000. - Harvey P. Dale, Jan 09 2016
a(19) > 20941. - Jinyuan Wang, Dec 27 2019
MATHEMATICA
Do[ If[ PrimeQ[ (10*7^n -1)/3 ], Print[ n ] ], {n, 0, 2500} ]
Select[Range[0, 1900], PrimeQ[(10*7^#-1)/3]&] (* Harvey P. Dale, Jan 09 2016 *)
PROG
(PARI) is(n)=ispseudoprime((10*7^n-1)/3) \\ Charles R Greathouse IV, Jun 13 2017
CROSSREFS
Cf. A057437.
Sequence in context: A189331 A157023 A101554 * A038341 A075718 A259710
KEYWORD
nonn,more
AUTHOR
Robert G. Wilson v, Sep 09 2000
EXTENSIONS
a(18) from Jinyuan Wang, Dec 27 2019
a(19) from Michael S. Branicky, Jul 11 2024
STATUS
approved