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%I #18 Jan 17 2019 13:44:06
%S 1,4,7,16,19,64,82,89,107,251,334,1487,6355,65711,96797
%N Indices of primes in sequence defined by A(0) = 69, A(n) = 10*A(n-1) - 31 for n > 0.
%C Numbers n such that (590*10^n + 31)/9 is prime.
%C Numbers n such that digit 6 followed by n >= 0 occurrences of digit 5 followed by digit 9 is prime.
%C Numbers corresponding to terms <= 334 are certified primes.
%C Next term, if it exists, is bigger than 3000. - _Stefan Steinerberger_, Feb 03 2006
%C a(16) > 10^5. - _Robert Price_, Sep 13 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/6/65559.htm#prime">Prime numbers of the form 655...559</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A103041(n) - 1.
%e 655559 is prime, hence 4 is a term.
%t For[n=1, n<= 3000, n++, If[PrimeQ[(590*10^n + 31)/9], Print[n]]] (Steinerberger)
%o (PARI) a=69;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a-31)
%o (PARI) for(n=0,1500,if(isprime((590*10^n+31)/9),print1(n,",")))
%Y Cf. A000533, A002275, A103041.
%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_, Feb 03 2006
%E 6355 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
%E a(14)-a(15) from _Robert Price_, Sep 13 2015
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