A237263 Smallest prime such that if up to n copies of the final digit are appended to the number, it remains prime, but it does not for n+1 copies.
2, 31, 19, 23, 139, 6089, 40949, 13153513, 748105003, 11307204673, 202073177599, 14740352606699
Offset: 0
Examples
23 is prime, so are 233, 2333, 23333, but not 233333 = 353 * 661. No prime smaller than 23 has this property for n = 3, so a(3) = 23.
Links
- D. J. Broadhurst et al., Prime Numbers and Primality Testing, Topic 25454, Yahoo Groups, 2014
- David Broadhurst, Kevin Acres, Mark Underwood, Base-10 puzzle, digest of 6 messages in primenumbers Yahoo group, Jan 16 - Feb 1, 2014.
Extensions
a(1)-a(10) from David Broadhurst, Feb 01 2014
a(11) from Giovanni Resta, Feb 06 2014