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