OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 6 followed by k-2 occurrences of the digit 3 followed by the digits 83 is prime (see Example section).
a(24) > 2*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 63w83.
EXAMPLE
5 is in this sequence because (19*10^5+149)/3 = 633383 is prime.
Initial terms and associated primes:
a(1) = 1, 113;
a(2) = 2, 683;
a(3) = 5, 633383;
a(4) = 7, 63333383;
a(5) = 8, 633333383; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(19*10^# + 149)/3] &]
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Apr 29 2017
EXTENSIONS
a(23) from Robert Price, May 17 2019
STATUS
approved