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A101736 Indices of primes in sequence defined by A(0) = 47, A(n) = 10*A(n-1) + 17 for n > 0. 1

%I

%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

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Last modified July 12 04:30 EDT 2020. Contains 335658 sequences. (Running on oeis4.)