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%I #19 Jan 17 2019 13:44:05
%S 1,245,1139,10393,43879
%N Indices of primes in sequence defined by A(0) = 99, A(n) = 10*A(n-1) - 71 for n > 0.
%C Numbers n such that (820*10^n + 71)/9 is a prime.
%C Numbers n such that digit 9 followed by n >= 0 occurrences of digit 1 followed by digit 9 is prime.
%C Numbers corresponding to terms <= 1139 are certified primes. For number corresponding to 10393 and larger see P. De Geest, PDP Reference Table.
%D Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
%H Patrick De Geest, <a href="http://www.worldofnumbers.com/deplat.htm#pdp919">PDP Reference Table - 919</a>.
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/9/91119.htm#prime">Prime numbers of the form 911...119</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A082717(n) - 2.
%e 919 is prime, hence 1 is a term.
%t Flatten[Position[NestList[10#-71&,99,1200],_?PrimeQ]]-1 (* _Harvey P. Dale_, May 02 2012 *)
%o (PARI) a=99;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a-71)
%o (PARI) for(n=0,1500,if(isprime((820*10^n+71)/9),print1(n,",")))
%Y Cf. A000533, A002275, A082717.
%K nonn,hard
%O 1,2
%A _Robert G. Wilson v_, Aug 18 2000
%E Additional comments from _Klaus Brockhaus_ and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Nov 27 2004
%E Edited by _N. J. A. Sloane_, Jun 15 2007
%E One more term from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
%E Edited comments section by _Patrick De Geest_, Nov 02 2014
%E Edited by _Ray Chandler_, Nov 04 2014
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