OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digits 44 followed by k-1 occurrences of the digit 8 followed by the digit 3 is prime (see Example section).
a(21) > 2*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 448w3.
EXAMPLE
2 is in this sequence because (404*10^2 - 53)/9 = 4483 is prime.
Initial terms and associated primes:
a(1) = 1, 443;
a(2) = 2, 4483;
a(3) = 4, 448883;
a(4) = 8, 4488888883;
a(5) = 22, 448888888888888888888883; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(404*10^# - 53)/9] &]
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Nov 24 2017
STATUS
approved