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%I #17 Jan 17 2019 13:44:06
%S 29,40,227,580,1289,2579,3695,11389,21557
%N Indices of primes in sequence defined by A(0) = 93, A(n) = 10*A(n-1) + 13 for n > 0.
%C Numbers n such that (850*10^n - 13)/9 is prime.
%C Numbers n such that digit 9 followed by n >= 0 occurrences of digit 4 followed by digit 3 is prime.
%C Numbers corresponding to terms <= 580 are certified primes.
%C a(10) > 10^5. - _Robert Price_, Nov 05 2015
%D Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/9/94443.htm#prime">Prime numbers of the form 944...443</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A103098(n) - 1.
%e 9444444444444444444444444444443 is prime, hence 29 is a term.
%t Select[Range[0, 100000], PrimeQ[(850*10^# - 13)/9] &] (* _Robert Price_, Nov 05 2015 *)
%o (PARI) a=93;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a+13)
%o (PARI) for(n=0,1500,if(isprime((850*10^n-13)/9),print1(n,",")))
%Y Cf. A000533, A002275, A103098.
%K nonn,hard,more,less
%O 1,1
%A _Klaus Brockhaus_ and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Nov 27 2004
%E More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
%E a(8)-a(9) from Kamada data by _Ray Chandler_, Apr 28 2015
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