OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 8 followed by k-2 occurrences of the digit 3 followed by the digits 11 is prime (see Example section).
a(26) > 2*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 83w11.
EXAMPLE
2 is in this sequence because (25*10^2 - 67)/3 = 811 is prime.
Initial terms and associated primes:
a(1) = 1, 61;
a(2) = 2, 811;
a(3) = 3, 8311;
a(4) = 4, 83311;
a(5) = 39, 8333333333333333333333333333333333333311; etc.
MATHEMATICA
Select[Range[1, 100000], PrimeQ[(25*10^# - 67)/3] &]
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Nov 10 2017
EXTENSIONS
a(23)-a(25) from Robert Price, Jun 19 2019
STATUS
approved