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%I #31 Sep 08 2022 08:45:16
%S 0,1,2,3,6,12,20,21,37,42,55,60,98,100,104,223,237,260,501,570,600,
%T 698,8857,20911,24345,31964,67742,162924
%N Numbers n such that 8*10^n + 9 is prime.
%C a(29) > 2*10^5. - _Robert Price_, Dec 18 2015
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/8/80009.htm#prime">Prime numbers of the form 800...009</a>.
%H Sabin Tabirca and Kieran Reynolds, <a href="http://multimedia.ucc.ie/Staff/ST/articles/SNJ03_Tabirca1.ps">Lacunary Prime Numbers</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A101057(n-1) + 1, for n>1.
%e For n =0, 8*10^0 + 9 = 8 + 9 = 17, hence 0 is a term.
%t Do[ If[ PrimeQ[ 8*10^n + 9], Print[ n ]], {n, 0, 10000}]
%o (PARI) for(n=0, 1e3, if(ispseudoprime(8*10^n + 9), print1(n, ", "))) \\ _Altug Alkan_, Dec 18 2015
%o (Magma) [n: n in [0..3*10^2] | IsPrime(8*10^n + 9)]; // _Vincenzo Librandi_, Dec 20 2015
%Y Cf. A101057.
%K more,nonn
%O 1,3
%A _Robert G. Wilson v_, Jan 19 2005
%E a(23)-a(26) from Kamada data by _Robert Price_, Dec 14 2010
%E a(1) = 0 inserted and a(28) added by _Robert Price_, Dec 18 2015