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%I #35 Nov 03 2019 19:39:48
%S 7,73,97,115,205,985,1227,4795,20721,133581,411591
%N Numbers k such that (89*10^(k-1) + 1)/9 is a depression prime.
%C Prime versus probable prime status and proofs are given in the author's table.
%C No other terms below 700000. - _Serge Batalov_, Sep 22 2014
%D C. Caldwell and H. Dubner, "Journal of Recreational Mathematics", Volume 28, No. 1, 1996-97, pp. 1-9.
%H Patrick De Geest, <a href="http://www.worldofnumbers.com/deplat.htm#pdp989">PDP Reference Table - 989</a>.
%H Makoto Kamada <a href="https://stdkmd.net/nrr/9/98889.htm#prime">Prime numbers of the form 988...889</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%e k=7 -> (89*10^(7-1) + 1)/9 = 8*(10^7 - 1)/9 + (10^6 + 1) = 8888888 + 1000001 = 9888889.
%Y Cf. A082697-A082719, A056266.
%K nonn,base,more
%O 1,1
%A _Patrick De Geest_, Apr 13 2003
%E Additional PRP term 133581 from _Serge Batalov_, May 15 2010
%E Additional PRP term 411591 from _Serge Batalov_, Sep 22 2014
%E Edited by _Ray Chandler_, Nov 05 2014
%E Definition revised by _N. J. A. Sloane_, Oct 30 2019
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