OFFSET
1,2
COMMENTS
For k > 0, numbers k such that the digits 88 followed by k-1 occurrences of the digit 9 followed by the digit 3 is prime (see Example section).
a(30) > 2*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 889w3.
EXAMPLE
3 is in this sequence because 89*10^3 - 7 = 88993 is prime.
Initial terms and associated primes:
a(1) = 1, 883;
a(2) = 2, 8893;
a(3) = 3, 88993;
a(4) = 19, 889999999999999999993;
a(5) = 33, 88999999999999999999999999999999993; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[89*10^# - 7] &]
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Mar 02 2017
EXTENSIONS
a(28)-a(29) from Robert Price, Apr 23 2020
STATUS
approved