OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digits 99 followed by k-1 occurrences of the digit 6 followed by the digit 1 is prime (see Example section).
a(29) > 3*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 996w1.
EXAMPLE
3 is in this sequence because (299*10^3 - 17) / 3 = 99661 is prime.
Initial terms and associated primes:
a(1) = 1, 991;
a(2) = 3, 99661;
a(3) = 6, 99666661;
a(4) = 12, 99666666666661;
a(5) = 16, 996666666666666661; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(299*10^# - 17) / 3] &]
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Jan 13 2017
EXTENSIONS
a(26)-a(27) from Robert Price, Apr 15 2020
Constant 229 corrected to 299 by Georg Fischer, Jun 26 2020
a(28) from Robert Price, Jun 21 2023
STATUS
approved