OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 8 followed by k-2 occurrences of the digit 6 followed by the digits 83 is prime (see Example section).
a(27) > 3*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 86w83.
EXAMPLE
2 is in this sequence because (26*10^2 + 49)/3 = 883 is prime.
Initial terms and associated primes:
a(1) = 1, 103;
a(2) = 2, 883;
a(3) = 5, 866683;
a(4) = 6, 8666683;
a(5) = 18, 8666666666666666683; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(26*10^# + 49)/3] &]
PROG
(PARI) isok(k) = isprime((26*10^k + 49)/3); \\ Michel Marcus, Feb 18 2017
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Feb 17 2017
EXTENSIONS
a(26) from Robert Price, Jul 31 2019
STATUS
approved