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 17 is prime (see Example section).
a(30) > 3*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 63w17.
EXAMPLE
3 is in this sequence because (19*10^3 - 49)/3 = 6317 is prime.
Initial terms and associated primes:
a(1) = 1, 47;
a(2) = 2, 617;
a(3) = 3, 6317;
a(4) = 4, 63317;
a(5) = 5, 633317; etc.
MATHEMATICA
Select[Range[1, 100000], PrimeQ[(19*10^# - 49)/3] &]
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Feb 06 2017
EXTENSIONS
a(25)-a(28) from Robert Price, May 18 2019
a(29) from Robert Price, Jun 17 2023
STATUS
approved