OFFSET
1,2
COMMENTS
For k>1, numbers k such that the digits 59 followed by k-1 occurrences of the digit 5 followed by the digit 3 is prime (see Example section).
a(23) > 2*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 595w3.
EXAMPLE
2 is in this sequence because (536*10^2 - 23)/9 = 5953 is prime.
Initial terms and associated primes:
a(1) = 1, 593;
a(2) = 2, 5953;
a(3) = 5, 5955553;
a(4) = 7, 595555553;
a(5) = 8, 5955555553; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(536*10^# - 23)/9] &]
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Nov 05 2017
EXTENSIONS
a(21)-a(22) from Robert Price, Feb 23 2020
STATUS
approved