A103026 - OEIS

%I #26 Jan 17 2019 13:44:07

%S 0,1,2,3,8,9,19,58,121,187,806,855,1019,2593,2749,3016,4295,9664,

%T 14927,34562,64387,71299,71951

%N Numbers n such that 6*10^n+7 is prime.

%C a(24) > 2*10^5. - _Robert Price_, Sep 17 2015

%H Makoto Kamada, <a href="https://stdkmd.net/nrr/6/60007.htm#prime">Prime numbers of the form 600...007</a>.

%H Sabin Tabirca and Kieran Reynolds, <a href="http://multimedia.ucc.ie/Staff/ST/articles/SNJ03_Tabirca1.ps">Lacunary Prime Numbers</a>.

%F a(n) = A101518(n-1) + 1 for n>1. - _L. Edson Jeffery_, Nov 28 2013

%t Do[ If[ PrimeQ[6*10^n + 7], Print[n]], {n, 0, 10000}]

%o (PARI) is(n)=ispseudoprime(6*10^n+7) \\ _Charles R Greathouse IV_, Jun 12 2017

%Y Cf. A101518.

%K nonn,more,hard

%O 1,3

%A _Robert G. Wilson v_, Jan 18 2005

%E a(19)-a(23) from Kamada link by _Ray Chandler_, Jan 04 2011

%E Inserted a(1)=0 by _Robert Price_, Sep 17 2015