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%I #17 Jan 17 2019 13:44:06
%S 22,52,12808,15070
%N Indices of primes in sequence defined by A(0) = 57, A(n) = 10*A(n-1) - 53 for n > 0.
%C Numbers n such that (460*10^n + 53)/9 is prime.
%C Numbers n such that digit 5 followed by n >= 0 occurrences of digit 1 followed by digit 7 is prime.
%C Numbers corresponding to terms <= 52 are certified primes. No further terms up to 2400.
%C a(5) > 10^5. - _Robert Price_, Jun 20 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/5/51117.htm#prime">Prime numbers of the form 511...117</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A103006(n+1) - 1.
%e 511111111111111111111117 is prime, hence 22 is a term.
%o (PARI) a=57;for(n=0,1000,if(isprime(a),print1(n,","));a=10*a-53)
%o (PARI) for(n=0,1000,if(isprime((460*10^n+53)/9),print1(n,",")))
%Y Cf. A000533, A002275, A103006.
%K nonn,more
%O 1,1
%A _Klaus Brockhaus_ and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 09 2004
%E a(3)-a(4) from Kamada data by _Ray Chandler_, Apr 30 2015
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