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%I #17 Jan 17 2019 13:44:06
%S 1,2,7,49,55,71,107,131,181,1099,1367,1604,5131,22681
%N Indices of primes in sequence defined by A(0) = 63, A(n) = 10*A(n-1) + 53 for n > 0.
%C Numbers n such that (620*10^n - 53)/9 is prime.
%C Numbers n such that digit 6 followed by n >= 0 occurrences of digit 8 followed by digit 3 is prime.
%C Numbers corresponding to terms <= 181 are certified primes.
%C a(15) > 10^5. - _Robert Price_, Sep 15 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/6/68883.htm#prime">Prime numbers of the form 688...883</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A103045(n) - 1.
%e 683 is prime, hence 1 is a term.
%t Flatten[Position[NestList[10#+53&,63,1700],_?(PrimeQ[#]&)]]-1 (* _Harvey P. Dale_, Sep 24 2013 *)
%o (PARI) a=63;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a+53)
%o (PARI) for(n=0,1500,if(isprime((620*10^n-53)/9),print1(n,",")))
%Y Cf. A000533, A002275, A103045.
%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(14) from Kamada data by _Ray Chandler_, Apr 30 2015
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