%I #15 Jan 17 2019 13:44:06
%S 0,1,6,13,24,115,426,594,636,775,1705,16627,55557
%N Indices of primes in sequence defined by A(0) = 47, A(n) = 10*A(n-1) + 17 for n > 0.
%C Numbers n such that (440*10^n - 17)/9 is prime.
%C Numbers n such that digit 4 followed by n >= 0 occurrences of digit 8 followed by digit 7 is prime.
%C Numbers corresponding to terms <= 775 are certified primes.
%C a(14) > 10^5. - _Robert Price_, Jun 05 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/4/48887.htm#prime">Prime numbers of the form 488...887</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A102999(n) - 1.
%e 487 is prime, hence 1 is a term.
%t For[n=0, n<= 3000, n++, If[PrimeQ[(440*10^n - 17)/9], Print[n]]] (Steinerberger)
%o (PARI) a=47;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a+17)
%o (PARI) for(n=0,1500,if(isprime((440*10^n-17)/9),print1(n,",")))
%Y Cf. A000533, A002275, A102999.
%K nonn,hard
%O 1,3
%A _Klaus Brockhaus_ and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 14 2004
%E a(11) from _Stefan Steinerberger_, Feb 04 2006
%E a(12) from Kamada data by _Ray Chandler_, May 01 2015
%E a(13) from _Robert Price_, Jun 05 2015