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Numbers k such that (15*10^(k-1) - 51)/9 is a plateau prime.
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%I #28 Nov 09 2019 03:13:48

%S 5,13,17,19,37,53,73,101,6233,24029,40223,66395

%N Numbers k such that (15*10^(k-1) - 51)/9 is a plateau 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#pdp161">PDP Reference Table - 161</a>.

%H Makoto Kamada, <a href="https://stdkmd.net/nrr/1/16661.htm#prime">Prime numbers of the form 166...661</a>.

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

%F a(n) = A056247(n+1) + 2.

%e k=13 -> (15*10^(13-1) - 51)/9 = 1666666666661.

%o (PARI) is(n)=ispseudoprime(2*(10^n-1)/3-5*(10^(n-1)+1)) || ispseudoprime(15*10^(n-1)-51)/9 \\ _Charles R Greathouse IV_, Feb 07 2013

%Y Cf. A056247, A068647, A082697-A082720.

%K nonn,base,more

%O 1,1

%A _Patrick De Geest_, Apr 13 2003

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

%E Edited by _Ray Chandler_, Nov 04 2014