%I #18 Mar 27 2020 20:10:14

%S 5,7,55,97,455,575,3385,11441,12625,19447,35461,81215,95327

%N Numbers n such that 2*(10^n-1)/3+(10^(n-1)+1) or (69*10^(n-1)+3)/9 is a plateau or depression prime.

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

%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#pdp767">PDP Reference Table - 767</a>.

%H Makoto Kamada, <a href="https://stdkmd.net/nrr/7/76667.htm#prime">Prime numbers of the form 766...667</a>.

%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.

%e 7 is a term because 2*(10^7-1)/3+(10^6+1) = 7666667.

%Y Cf. A082697-A082720, A056260.

%K nonn,base,more

%O 1,1

%A _Patrick De Geest_, Apr 13 2003

%E 35461 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008

%E Added two more terms from PDP table, by _Patrick De Geest_, Nov 04 2014

%E Edited by _Ray Chandler_, Nov 05 2014

%E Name clarified by _Michel Marcus_, Mar 27 2020