OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 6 followed by k-2 occurrences of the digit 0 followed by the digits 17 is prime (see Example section).
a(24) > 2*10^5.
If k is odd then 6*10^k + 17 is divisible by 11. - David Radcliffe, Sep 04 2018
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 60w17.
EXAMPLE
4 is in this sequence because 6*10^4 + 17 = 60017 is prime.
Initial terms and associated primes:
a(1) = 0, 23;
a(2) = 2, 617;
a(3) = 4, 60017;
a(4) = 8, 600000017;
a(5) = 40, 60000000000000000000000000000000000000017; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ{6*10^# + 17] &]
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Apr 23 2017
EXTENSIONS
a(23) from Robert Price, Apr 07 2019
STATUS
approved