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 A102009 Indices of primes in sequence defined by A(0) = 13, A(n) = 10*A(n-1) - 7 for n > 0. 1

%I

%S 0,2,8,47,57,152,260,875,1178,1595,17714,63717

%N Indices of primes in sequence defined by A(0) = 13, A(n) = 10*A(n-1) - 7 for n > 0.

%C Numbers n such that (110*10^n + 7)/9 is prime.

%C Numbers n such that digit 1 followed by n >= 0 occurrences of digit 2 followed by digit 3 is prime.

%C Numbers corresponding to terms <= 875 are certified primes.

%C a(13) > 10^5. - _Robert Price_, Nov 15 2014

%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/1/12223.htm#prime">Prime numbers of the form 122...223</a>.

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

%F a(n) = A102929(n+1) - 1. - _Robert Price_, Nov 15 2014

%e 1223 is prime, hence 2 is a term.

%o (PARI) a=13;for(n=0,1600,if(isprime(a),print1(n,","));a=10*a-7)

%o (PARI) for(n=0,1600,if(isprime((110*10^n+7)/9),print1(n,",")))

%Y Cf. A000533, A002275, A102929.

%K nonn,hard,more

%O 1,2

%A _Klaus Brockhaus_ and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 28 2004

%E a(11)-a(12) derived from A102929 by _Robert Price_, Nov 15 2014

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Last modified October 22 18:50 EDT 2019. Contains 328319 sequences. (Running on oeis4.)