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A101733 Indices of primes in sequence defined by A(0) = 49, A(n) = 10*A(n-1) - 11 for n > 0. 1

%I

%S 1,3,25,1270,1411,3327,4675,47050,67663

%N Indices of primes in sequence defined by A(0) = 49, A(n) = 10*A(n-1) - 11 for n > 0.

%C Numbers n such that (430*10^n + 11)/9 is a prime.

%C Numbers n such that digit 4 followed by n >= 0 occurrences of digit 7 followed by digit 9 is a prime.

%C Some of the larger entries may only correspond to probable primes.

%C a(10) > 10^5. - _Robert Price_, Jun 01 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/4/47779.htm#prime">Prime numbers of the form 477...779</a>.

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

%F a(n) = A102996(n) - 1.

%e 47779 is a prime, hence 3 is a term.

%t Select[Range[0, 1000], PrimeQ[(430*10^# + 11)/9] &] (* _Robert Price_, Jun 01 2015 *)

%o (PARI) a=49;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a-11)

%o (PARI) for(n=0,1500,if(isprime((430*10^n+11)/9),print1(n,",")))

%Y Cf. A000533, A002275, A102996.

%K nonn,hard,more

%O 1,2

%A _Klaus Brockhaus_ and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 14 2004

%E More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008

%E a(8) from Erik Branger May 01 2013 by _Ray Chandler_, May 01 2015

%E a(9) from _Robert Price_, Jun 01 2015

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Last modified August 22 00:43 EDT 2019. Contains 326169 sequences. (Running on oeis4.)