OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 9 followed by k-2 occurrences of the digit 0 followed by the digits 59 is prime (see Example section).
a(25) > 2*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 90w59.
EXAMPLE
3 is in this sequence because 9*10^3 + 59 = 9059 is prime.
Initial terms and associated primes:
a(1) = 1, 149;
a(2) = 3, 9059;
a(3) = 4, 90059;
a(4) = 6, 9000059;
a(5) = 7, 90000059; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[9*10^# + 59] &]
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Oct 06 2017
EXTENSIONS
a(23)-a(24) from Robert Price, Jan 13 2020
STATUS
approved