%I #12 Jan 17 2019 13:44:06

%S 0,12,72,126

%N Indices of primes in sequence defined by A(0) = 67, A(n) = 10*A(n-1) - 43 for n > 0.

%C Numbers n such that (560*10^n + 43)/9 is prime.

%C Numbers n such that digit 6 followed by n >= 0 occurrences of digit 2 followed by digit 7 is prime.

%C Numbers corresponding to terms <= 126 are certified primes.

%C a(5) > 10^5. - _Robert Price_, Sep 12 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/6/62227.htm#prime">Prime numbers of the form 622...227</a>.

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

%F a(n) = A097402(n+1) - 1.

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

%t Select[Range[0, 100000], PrimeQ[(560 * 10^# + 43)/9] &] (* _Robert Price_, Sep 12 2015 *)

%o (PARI) a=67;for(n=0,1000,if(isprime(a),print1(n,","));a=10*a-43)

%o (PARI) for(n=0,1000,if(isprime((560*10^n+43)/9),print1(n,",")))

%Y Cf. A000533, A002275, A097402.

%K nonn,hard,more

%O 1,2

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