OFFSET
1,1
COMMENTS
For k > 1, numbers k such that the digit 2 followed by k-2 occurrences of the digit 9 followed by the digits 03 is prime (see Example section).
a(32) > 3*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 29w03.
EXAMPLE
5 is in this sequence because 3*10^5 - 97 = 299903 is prime.
Initial terms and associated primes:
a(1) = 3, 2903;
a(2) = 5, 299903;
a(3) = 6, 2999903;
a(4) = 7; 29999903;
a(5) = 28, 29999999999999999999999999903; etc.
MATHEMATICA
Select[Range[2, 100000], PrimeQ[3*10^# - 97] &]
PROG
(PARI) isok(n) = isprime(3*10^n - 97); \\ Michel Marcus, Aug 07 2017
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Aug 06 2017
EXTENSIONS
a(27)-a(30) from Robert Price, Jul 18 2018
a(31) from Robert Price, Jun 17 2023
STATUS
approved