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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 (list; graph; refs; listen; history; text; internal format)
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.

LINKS

Table of n, a(n) for n=1..11.

Patrick De Geest, PDP Reference Table - 989.

Makoto Kamada Prime numbers of the form 988...889.

Index entries for primes involving repunits.

EXAMPLE

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

CROSSREFS

Cf. A082697-A082719, A056266.

Sequence in context: A157920 A321077 A080794 * A188465 A142053 A012049

Adjacent sequences:  A082716 A082717 A082718 * A082720 A082721 A082722

KEYWORD

nonn,base,more,changed

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

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Last modified November 13 08:18 EST 2019. Contains 329093 sequences. (Running on oeis4.)