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%I #15 Jan 17 2019 13:44:06
%S 1,259,416,952,2137,2968,3044,11776,23647
%N Indices of primes in sequence defined by A(0) = 69, A(n) = 10*A(n-1) - 71 for n > 0.
%C Numbers n such that (550*10^n + 71)/9 is prime.
%C Numbers n such that digit 6 followed by n >= 0 occurrences of digit 1 followed by digit 9 is prime.
%C Numbers corresponding to terms <= 952 are certified primes.
%C a(10) > 10^5. - _Robert Price_, Sep 08 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/6/61119.htm#prime">Prime numbers of the form 611...119</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A103029(n) - 1.
%e 619 is prime, hence 1 is a term.
%t Select[Range[0, 10000], PrimeQ[(550*10^# + 71)/9] &] (* _Robert Price_, Sep 08 2015 *)
%o (PARI) a=69;for(n=0,1000,if(isprime(a),print1(n,","));a=10*a-71)
%o (PARI) for(n=0,1000,if(isprime((550*10^n+71)/9),print1(n,",")))
%Y Cf. A000533, A002275, A103029.
%K nonn,hard,more
%O 1,2
%A _Klaus Brockhaus_ and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 06 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 30 2015
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