OFFSET
1,3
COMMENTS
For k > 1, numbers k such that the digit 9 followed by k-2 occurrences of the digit 3 followed by the digits 29 is prime (see Example section).
a(28) > 3*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 93w29.
EXAMPLE
2 is in this sequence because (28*10^2 - 13) / 3 = 929 is prime.
Initial terms and associated primes:
a(1) = 0, 5;
a(2) = 1, 89;
a(3) = 2, 929;
a(4) = 4, 93329;
a(5) = 5, 933329, etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(28*10^# - 13) / 3] &]
PROG
(PARI) is(n)=ispseudoprime((28*10^n - 13)/3) \\ Charles R Greathouse IV, Jun 13 2017
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, Sep 23 2016
STATUS
approved