OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 7 followed by k-2 occurrences of the digit 9 followed by the digits 33 is prime (see Example section).
a(23) > 2*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 79w33.
EXAMPLE
2 is in this sequence because 8*10^2 - 67 = 733 is prime.
Initial terms and associated primes:
a(1) = 1, 13;
a(2) = 2, 733;
a(3) = 3, 7933;
a(4) = 14, 799999999999933; etc.
MATHEMATICA
Select[Range[1, 100000], PrimeQ[8*10^# - 67] &]
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Oct 29 2017
EXTENSIONS
a(22) from Robert Price, Aug 05 2019
STATUS
approved