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 23 is prime (see Example section).
a(33) > 2*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 86w23.
EXAMPLE
3 is in this sequence because (26*10^3 - 131)/3 = 8623 is prime.
Initial terms and associated primes:
a(1) = 1, 43;
a(2) = 2, 823;
a(3) = 3, 8623;
a(4) = 5, 866623;
a(5) = 7, 86666623, etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(26*10^# - 131)/3] &]
PROG
(PARI) isok(n) = isprime((26*10^n - 131)/3); \\ Michel Marcus, Apr 28 2016
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, Apr 28 2016
EXTENSIONS
a(30)-a(32) from Robert Price, Oct 19 2019
STATUS
approved