A183177 - OEIS

%I #20 Jan 17 2019 13:44:08

%S 1,7,85,94,273,356,1077,1797,6758,30232

%N Numbers n such that (10^(2n+1)+15*10^n-1)/3 is prime.

%C a(11) > 10^5. - _Robert Price_, Apr 21 2016

%D C. Caldwell and H. Dubner, "Journal of Recreational Mathematics", Volume 28, No. 1, 1996-97, pp. 1-9.

%H Patrick De Geest, World!Of Numbers, <a href="http://www.worldofnumbers.com/wing.htm#pwp383">Palindromic Wing Primes (PWP's)</a>

%H Makoto Kamada, <a href="https://stdkmd.net/nrr/3/33833.htm#prime">Prime numbers of the form 33...33833...33</a>

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

%F a(n) = (A077792(n)-1)/2.

%t Do[If[PrimeQ[(10^(2n + 1) + 15*10^n - 1)/3], Print[n]], {n, 3000}]

%o (PARI) is(n)=ispseudoprime((10^(2*n+1)+15*10^n-1)/3) \\ _Charles R Greathouse IV_, Jun 13 2017

%Y Cf. A004023, A077775-A077798, A107123-A107127, A107648, A107649, A115073, A183174-A183187.

%K nonn,more,base

%O 1,2

%A _Ray Chandler_, Dec 28 2010

%E a(10) from _Robert Price_, Apr 21 2016