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 41 is prime (see Example section).
a(32) > 3*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 86w41.
EXAMPLE
3 is in this sequence because (26*10^3 - 77)/3 = 8641 is prime.
Initial terms and associated primes:
a(1) = 1, 61;
a(2) = 3, 8641;
a(3) = 5, 866641;
a(4) = 7, 86666641;
a(5) = 11, 866666666641; etc.
MATHEMATICA
Select[Range[1, 100000], PrimeQ[(26*10^# - 77)/3] &]
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Feb 22 2017
EXTENSIONS
a(26)-a(28) from Robert Price, Nov 15 2019
a(29)-a(31) from Robert Price, Jul 12 2023
STATUS
approved