OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 2 followed by k-2 occurrences of the digit 3 followed by the digits 29 is prime (see Example section).
a(32) > 2*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 23w29.
EXAMPLE
5 is in this sequence because (7*10^5 - 13)/3 = 233329 is prime.
Initial terms and associated primes:
a(1) = 1, 19;
a(2) = 2, 229;
a(3) = 5, 233329;
a(4) = 6, 2333329;
a(5) = 28, 23333333333333333333333333329, etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(7*10^# - 13)/3] &]
PROG
(PARI) is(n)=ispseudoprime((7*10^n - 13)/3) \\ Charles R Greathouse IV, Jun 08 2016
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, Jun 04 2016
EXTENSIONS
a(30)-a(31) from Robert Price, Jul 13 2018
STATUS
approved