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%I #22 Jan 17 2019 13:44:07
%S 0,3,6,18,30,88,93,154,177,228,573,897,981,1416,1450,3366,4932,5194,
%T 13479,18609,23346,51424,74676,80571
%N Numbers n such that 9*10^n + 5*R_n - 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
%C Also numbers n such that (86*10^n-41)/9 is prime.
%C a(25) > 10^5. - _Robert Price_, Nov 10 2015
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/9/95551.htm#prime">Prime numbers of the form 955...551</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A101009(n-1) + 1, for n>1.
%e For n=0, (86*10^n - 41)/9 = 5 which is prime.
%t Do[ If[ PrimeQ[(86*10^n - 41)/9], Print[n]], {n, 0, 10000}]
%o (PARI) for(n=0, 1e3, if(ispseudoprime((86*10^n-41)/9), print1(n,", "))) \\ _Altug Alkan_, Nov 10 2015
%Y Cf. A002275, A101009.
%K more,nonn
%O 1,2
%A _Robert G. Wilson v_, Jan 19 2005
%E a(19)-a(21) from Kamada data by _Robert Price_, Dec 14 2010
%E Inserted a(1)=0 and added a(22)-a(24) by _Robert Price_, Nov 10 2015
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