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 91 is prime (see Example section).
a(35) > 3*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 93w91.
EXAMPLE
3 is in this sequence because (28*10^3 + 173)/3 = 9391 is prime.
Initial terms and associated primes:
a(1) = 0, 67;
a(2) = 1, 151;
a(3) = 2, 991;
a(4) = 3, 9391;
a(5) = 9, 9333333391, etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(28*10^# + 173)/3] &]
PROG
(PARI) is(n)=ispseudoprime((28*10^n + 173)/3) \\ Charles R Greathouse IV, Jun 13 2017
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, May 02 2016
EXTENSIONS
a(33) from Robert Price, Dec 25 2019
a(34) from Robert Price, Jul 02 2024
STATUS
approved