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 73 is prime (see Example section).
a(29) > 2*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 63w73.
EXAMPLE
3 is in this sequence because (19*10^3 + 119)/3 = 6373 is prime.
Initial terms and associated primes:
a(1) = 1, 103;
a(2) = 2, 673;
a(3) = 3, 6373;
a(4) = 8, 633333373;
a(5) = 10, 63333333373; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(19*10^# + 119)/3] &]
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Feb 11 2017
STATUS
approved