OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 3 followed by k-2 occurrences of the digit 6 followed by the digits 97 is prime (see Example section).
a(25) > 3*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 36w97.
EXAMPLE
3 is in this sequence because (11*10^3 + 91)/3 = 3697 is prime.
Initial terms and associated primes:
a(1) = 1, 67;
a(2) = 2, 397;
a(3) = 3, 3697;
a(4) = 4, 36697;
a(5) = 5, 366697; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(11*10^# + 91)/3] &]
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Feb 24 2017
EXTENSIONS
a(24) from Robert Price, Jul 12 2023
STATUS
approved