OFFSET
1,1
COMMENTS
For k >= 0, numbers k such that the digits 95 followed by k occurrences of the digit 1 is prime (see Example section).
a(27) > 2*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 951w.
EXAMPLE
3 is in this sequence because (856*10^3 - 1) / 9 = 95111 is prime.
Initial terms and associated primes:
a(1) = 2, 9511;
a(2) = 3, 95111;
a(3) = 5, 9511111;
a(4) = 8, 9511111111;
a(5) = 9, 95111111111; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(856*10^# - 1) / 9] &]
PROG
(PARI) is(n)=ispseudoprime((856*10^n - 1)/9) \\ Charles R Greathouse IV, Jun 13 2017
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Nov 18 2016
EXTENSIONS
a(26) from Robert Price, Mar 30 2020
STATUS
approved