A082719 Numbers k such that (89*10^(k-1) + 1)/9 is a depression prime.

7, 73, 97, 115, 205, 985, 1227, 4795, 20721, 133581, 411591

Offset: 1

Author

Patrick De Geest, Apr 13 2003

Keywords

• nonn
• base
• more

Comments

Prime versus probable prime status and proofs are given in the author's table.

No other terms below 700000. - Serge Batalov, Sep 22 2014

Examples

			k=7 -> (89*10^(7-1) + 1)/9 = 8*(10^7 - 1)/9 + (10^6 + 1) = 8888888 + 1000001 = 9888889.
		

References

• C. Caldwell and H. Dubner, "Journal of Recreational Mathematics", Volume 28, No. 1, 1996-97, pp. 1-9.

Links

• Patrick De Geest, PDP Reference Table - 989.
• Makoto Kamada Prime numbers of the form 988...889.
• Index entries for primes involving repunits.

Crossrefs

Cf. A082697-A082719, A056266.

Extensions

Additional PRP term 133581 from Serge Batalov, May 15 2010

Additional PRP term 411591 from Serge Batalov, Sep 22 2014

Edited by Ray Chandler, Nov 05 2014

Definition revised by N. J. A. Sloane, Oct 30 2019