OFFSET
1,3
COMMENTS
Numbers k such that the digits 29 followed by k occurrences of the digit 3 is prime (see Example section).
a(24) > 2*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 293w.
EXAMPLE
3 is in this sequence because (88*10^3 - 1)/3 = 29333 is prime.
Initial terms and associated primes:
a(1) = 0, 29;
a(2) = 1, 293;
a(3) = 3, 29333;
a(4) = 6, 29333333;
a(5) = 9, 29333333333; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(88*10^# - 1)/3] &]
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Oct 11 2017
EXTENSIONS
a(23) from Robert Price, Apr 05 2020
STATUS
approved