OFFSET
1,3
COMMENTS
For k > 1, numbers k such that the digit 4 followed by k-2 occurrences of the digit 0 followed by the digits 19 is prime (see Example section).
a(37) > 3*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 40w19.
EXAMPLE
3 is in this sequence because 4*10^3 + 19 = 4019 is prime.
Initial terms and associated primes:
a(1) = 0, 23;
a(2) = 1, 59;
a(3) = 2, 419;
a(4) = 3, 4019;
a(5) = 9, 4000000019, etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[4*10^# + 19] &]
PROG
(PARI) is(n)=ispseudoprime(4*10^n + 19) \\ Charles R Greathouse IV, Jun 13 2017
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, Apr 09 2016
EXTENSIONS
a(35)-a(36) from Robert Price, Oct 22 2018
STATUS
approved