OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 4 followed by k-2 occurrences of the digit 0 followed by the digits 79 is prime (see Example section).
a(29) > 2*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 40w79.
EXAMPLE
3 is in this sequence because 4*10^3 + 79 = 4079 is prime.
Initial terms and associated primes:
a(1) = 0, 83;
a(2) = 2, 479;
a(3) = 3, 4079;
a(4) = 6, 4000079;
a(5) = 8, 400000079; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[4*10^# + 79] &]
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Jan 25 2017
EXTENSIONS
a(28) from Robert Price, Aug 10 2018
STATUS
approved