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A082719
Numbers k such that (89*10^(k-1) + 1)/9 is a depression prime.
3
7, 73, 97, 115, 205, 985, 1227, 4795, 20721, 133581, 411591
OFFSET
1,1
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
REFERENCES
C. Caldwell and H. Dubner, "Journal of Recreational Mathematics", Volume 28, No. 1, 1996-97, pp. 1-9.
EXAMPLE
k=7 -> (89*10^(7-1) + 1)/9 = 8*(10^7 - 1)/9 + (10^6 + 1) = 8888888 + 1000001 = 9888889.
CROSSREFS
KEYWORD
nonn,base,more
AUTHOR
Patrick De Geest, Apr 13 2003
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
STATUS
approved