OFFSET
1,3
COMMENTS
For k > 0, numbers k such that the digits 82 followed by k-1 occurrences of the digit 8 followed by the digit 9 is prime (see Example section).
a(28) > 2*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 828w9.
EXAMPLE
3 is in this sequence because (746*10^3 + 1)/9 = 82889 is prime.
Initial terms and associated primes:
a(1) = 0, 83;
a(2) = 1, 829;
a(3) = 3, 82889;
a(4) = 4, 828889;
a(5) = 12, 82888888888889; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(746*10^# + 1)/9] &]
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Feb 15 2017
EXTENSIONS
a(25)-a(27) from Robert Price, Mar 22 2020
STATUS
approved