%I #16 Jan 17 2019 13:44:06

%S 0,32,71,176,191,324,416,731,1361,13946,14886,32705,63953,64782,82376

%N Indices of primes in sequence defined by A(0) = 67, A(n) = 10*A(n-1) + 17 for n > 0.

%C Numbers n such that (620*10^n - 17)/9 is prime.

%C Numbers n such that digit 6 followed by n >= 0 occurrences of digit 8 followed by digit 7 is prime.

%C Numbers corresponding to terms <= 731 are certified primes.

%C a(16) > 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/6/68887.htm#prime">Prime numbers of the form 688...887</a>.

%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.

%F a(n) = A103046(n+1) - 1.

%e 67 is prime, hence 0 is a term.

%t Select[Range[0, 300], PrimeQ[(620*10^# - 17)/9] &] (* _Robert Price_, Sep 15 2015 *)

%o (PARI) a=67;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a+17)

%o (PARI) for(n=0,1500,if(isprime((620*10^n-17)/9),print1(n,",")))

%Y Cf. A000533, A002275, A103046.

%K nonn,hard,more

%O 1,2

%A _Klaus Brockhaus_ and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 06 2004

%E a(10)-a(12) from Kamada data by _Ray Chandler_, Apr 30 2015

%E a(13)-a(15) from _Robert Price_, Sep 15 2015