OFFSET
1,1
COMMENTS
For k > 1, numbers k such that the digit 4 followed by k-2 occurrences of the digit 8 followed by the digits 33 is prime (see Example section).
a(24) > 2*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 48w33.
EXAMPLE
2 is in this sequence because (44*10^2 - 503)/9 = 433 is prime.
Initial terms and associated primes:
a(1) = 2, 433;
a(2) = 5, 488833;
a(3) = 8, 488888833;
a(4) = 10, 48888888833;
a(5) = 11, 488888888833; etc.
MATHEMATICA
Select[Range[2, 100000], PrimeQ[(44*10^# - 503)/9] &]
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Oct 23 2017
EXTENSIONS
a(22)-a(23) from Robert Price, Dec 23 2018
STATUS
approved