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%I #18 Sep 08 2022 08:45:16
%S 1,2,4,10,11,22,74,100,121,172,646,2014,2683,11699,19624
%N Indices of primes in sequence defined by A(0) = 63, A(n) = 10*A(n-1) - 17 for n > 0.
%C Numbers n such that (550*10^n + 17)/9 is prime.
%C Numbers n such that digit 6 followed by n >= 0 occurrences of digit 1 followed by digit 3 is prime.
%C Numbers corresponding to terms <= 646 are certified primes.
%C a(16) > 10^5 - _Robert Price_, Sep 09 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/6/61113.htm#prime">Prime numbers of the form 611...113</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A103027(n) - 1.
%e 611113 is prime, hence 4 is a term.
%t Select[Range[0, 100000], PrimeQ[(550*10^# + 17)/9] &] (* _Robert Price_, Sep 09 2015 *)
%o (PARI) a=63;for(n=0,1000,if(isprime(a),print1(n,","));a=10*a-17)
%o (PARI) for(n=0,1000,if(isprime((550*10^n+17)/9),print1(n,",")))
%o (Magma) [n: n in [0..500]| IsPrime((550*10^n + 17) div 9)]; // _Vincenzo Librandi_, Sep 10 2015
%Y Cf. A000533, A002275, A103027.
%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 _Stefan Steinerberger_, May 06 2007
%E a(14)-a(15) from Kamada data by _Ray Chandler_, Apr 30 2015
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