A057018 Numbers k such that (10*7^k -1)/3 is prime.

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

Links

Table of n, a(n) for n=1..19.

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

Adjacent sequences: A057015 A057016 A057017 * A057019 A057020 A057021

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