OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 9 followed by k-2 occurrences of the digit 4 followed by the digits 33 is prime (see Example section).
a(27) > 2*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 94w33.
EXAMPLE
3 is in this sequence because (85*10^3 - 103)/9 = 9433 is prime.
Initial terms and associated primes:
a(1) = 1, 83;
a(2) = 3, 9433;
a(3) = 4, 94433;
a(4) = 16, 94444444444444433;
a(5) = 28, 94444444444444444444444444433; etc.
MATHEMATICA
Select[Range[1, 100000], PrimeQ[85*10^# - 103)/9] &]
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Oct 06 2017
STATUS
approved