OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 9 followed by k-2 occurrences of the digit 0 followed by the digits 19 is prime (see Example section).
a(33) > 3*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 90w19.
EXAMPLE
4 is in this sequence because 9*10^4+19 = 90019 is prime.
Initial terms and associated primes:
a(1) = 1, 109;
a(2) = 2, 919;
a(3) = 4, 90019;
a(4) = 5, 900019;
a(5) = 10, 90000000019, etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[9*10^# + 19] &]
PROG
(PARI) is(n)=ispseudoprime(9*10^n + 19) \\ Charles R Greathouse IV, Jun 13 2017
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, May 03 2016
STATUS
approved