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
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