OFFSET
1,1
COMMENTS
For k > 1, numbers k such that the digit 1 followed by k-2 occurrences of the digit 4 followed by the digits 93 is prime (see Example section).
a(25) > 2*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 14w93.
EXAMPLE
3 is in this sequence because (13*10^3 + 437)/9 = 1493 is prime.
Initial terms and associated primes:
a(1) = 2, 193;
a(2) = 3, 1493;
a(3) = 6, 1444493;
a(4) = 14, 144444444444493;
a(5) = 17, 144444444444444493; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(13*10^# + 437)/9] &]
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Feb 12 2017
EXTENSIONS
a(23)-a(24) from Robert Price, Apr 14 2018
STATUS
approved