OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 9 followed by k-2 occurrences of the digit 6 followed by the digits 41 is prime (see Example section).
a(31) > 2*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 96w41.
EXAMPLE
2 is in this sequence because (29*10^2 - 77) / 3 = 941 is prime.
Initial terms and associated primes:
a(1) = 1, 71;
a(2) = 2, 941;
a(3) = 12, 9666666666641;
a(4) = 14, 966666666666641;
a(5) = 32, 96666666666666666666666666666641; etc.
MATHEMATICA
Select[Range[1, 100000], PrimeQ[(29*10^# - 77) / 3] &]
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Jan 11 2017
EXTENSIONS
a(28)-a(30) from Robert Price, Jan 31 2020
STATUS
approved