OFFSET
1,3
COMMENTS
For k > 1, numbers k such that the digit 9 followed by k-2 occurrences of the digit 3 followed by the digits 71 is prime (see Example section).
a(41) > 3*10^5.
LINKS
Makoto Kamada, Search for 93w71.
EXAMPLE
3 is in this sequence because (28*10^3+113)/3 = 9371 is prime.
Initial terms and associated primes:
a(1) = 0, 47;
a(2) = 1, 131;
a(3) = 2, 971;
a(4) = 3, 9371;
a(5) = 4, 93371;
a(6) = 6, 9333371, etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(28*10^# + 113)/3] &]
PROG
(PARI) is(n)=ispseudoprime((28*10^n + 113)/3) \\ Charles R Greathouse IV, Jun 13 2017
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, Mar 31 2016
EXTENSIONS
a(37)-a(38) from Robert Price, Mar 13 2020
a(39)-a(40) from Robert Price, Jun 17 2023
STATUS
approved