OFFSET
1,3
COMMENTS
For k > 0, numbers k such that the digits 37 followed by k-1 occurrences of the digit 3 followed by the digit 9 is prime (see Example section).
a(31) > 3*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 373w9.
EXAMPLE
3 is in this sequence because (112*10^3+17)/3 = 37339 is prime.
Initial terms and associated primes:
a(1) = 0, 43;
a(2) = 1, 379:
a(3) = 2, 3739;
a(4) = 3, 37339;
a(5) = 4, 373339, etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(112*10^# + 17)/3] &]
PROG
(PARI) is(n)=ispseudoprime((112*10^n + 17)/3) \\ Charles R Greathouse IV, Jun 13 2017
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, May 14 2016
EXTENSIONS
a(29)-a(30) from Robert Price, Mar 05 2020
STATUS
approved