%I #27 Feb 01 2023 21:24:40
%S 3,13,15,31,105,127,343,601,9825
%N Numbers k such that (28*10^(k-1) + 17)/9 is a depression prime.
%C Prime versus probable prime status and proofs are given in the author's table.
%C a(10) > 2^16. - _Lucas A. Brown_, Apr 18 2021
%C a(10) > 2*10^5. - _Tyler Busby_, Feb 01 2023
%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#pdp313">PDP Reference Table - 313</a>.
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/3/31113.htm#prime">Prime numbers of the form 311...113</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A056251(n) + 2.
%e k=15 -> (28*10^(15-1) + 17)/9 = 311111111111113.
%Y Cf. A082697-A082720, A056251, A068650.
%K nonn,base,more
%O 1,1
%A _Patrick De Geest_, Apr 13 2003
%E Edited by _Ray Chandler_, Nov 04 2014