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 79 is prime (see Example section).
a(25) > 2*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 46w79.
EXAMPLE
2 is in this sequence because (14*10^2 + 37)/3 = 479 is prime.
Initial terms and associated primes:
a(1) = 0, 17;
a(2) = 1, 59;
a(3) = 2, 479;
a(4) = 3, 4679;
a(5) = 4, 46679; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(14*10^# + 37)/3] &]
PROG
(PARI) isok(k) = isprime((14*10^k + 37)/3); \\ Michel Marcus, Dec 30 2017
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Dec 29 2017
EXTENSIONS
a(22)-a(24) from Robert Price, Dec 05 2018
STATUS
approved