OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 4 followed by k-2 occurrences of the digit 6 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 46w33.
EXAMPLE
4 is in this sequence because (14*10^4 - 101)/3 = 46633 is prime.
Initial terms and associated primes:
a(1) = 1, 13;
a(2) = 2, 433;
a(3) = 4, 46633;
a(4) = 6, 4666633;
a(5) = 14, 466666666666633; etc.
MATHEMATICA
Select[Range[1, 100000], PrimeQ[(14*10^# - 101)/3] &]
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Apr 04 2017
EXTENSIONS
a(26) from Robert Price, Feb 23 2019
STATUS
approved