OFFSET
1,3
COMMENTS
For k > 1, numbers k such that the digit 4 followed by k-2 occurrences of the digit 6 followed by the digits 93 is prime (see Example section).
a(23) > 2*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 46w93.
EXAMPLE
1 is in this sequence because (14*10^1 + 79)/3 = 73 is prime.
Initial terms and associated primes:
a(1) = 0, 31;
a(2) = 1, 73;
a(3) = 6, 4666693;
a(4) = 7, 46666693;
a(5) = 8, 466666693; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(14*10^# + 79)/3] &] (* fixed by Shawn A. Broyles, Nov 27 2017 *)
PROG
(PARI) is(k) = ispseudoprime((14*10^k + 79)/3) \\ Iain Fox, Nov 27 2017
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Nov 25 2017
STATUS
approved