OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digits 10 followed by k occurrences of the digit 3 is prime (see Example section).
a(25) > 3*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 103w.
EXAMPLE
3 is in this sequence because (31*10^3 - 1)/3 = 10333 is prime.
Initial terms and associated primes:
a(1) = 1, 103;
a(2) = 2, 1033;
a(3) = 3, 10333;
a(4) = 4, 103333;
a(5) = 6, 10333333; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(31*10^# - 1)/3] &]
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Feb 28 2017
EXTENSIONS
a(23) from Robert Price, Feb 20 2020
a(24) from Robert Price, Jul 12 2023
STATUS
approved