OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 6 followed by k-2 occurrences of the digit 9 followed by the digits 77 is prime (see Example section).
a(36) > 3*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 69w77.
EXAMPLE
3 is in this sequence because 7*10^3 - 23 = 6977 is prime.
Initial terms and associated primes:
a(1) = 1, 47;
a(2) = 2, 677;
a(3) = 3, 6977;
a(4) = 23, 699999999999999999999977;
a(5) = 29, 699999999999999999999999999977, etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[7*10^# - 23] &]
PROG
(PARI) is(n)=ispseudoprime(7*10^n - 23) \\ Charles R Greathouse IV, Jun 13 2017
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, Apr 24 2016
EXTENSIONS
a(35) from Robert Price, Jul 27 2019
STATUS
approved