OFFSET
1,1
COMMENTS
Also, numbers k such that (7*10^k - 277)/9 is prime.
Terms from Kamada.
a(21) > 200000. - Tyler Busby, Apr 20 2024
LINKS
EXAMPLE
For k=5, 7*R_5 - 30 = 77777 - 30 = 77747 which is prime.
MATHEMATICA
Select[Range[0, 250000], PrimeQ[(7*10^# - 277)/9] &]
PROG
(Magma) [n: n in [2..500] | IsPrime((7*10^n-277) div 9)]; // Vincenzo Librandi, Apr 11 2015
CROSSREFS
KEYWORD
more,hard,nonn
AUTHOR
Robert Price, Apr 10 2015
EXTENSIONS
a(19)-a(20) from Kamada data by Tyler Busby, Apr 20 2024
STATUS
approved