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A101729 Indices of primes in sequence defined by A(0) = 41, A(n) = 10*A(n-1) + 51 for n > 0. 1

%I

%S 0,1,6,8,13,23,44,48,72,73,231,337,396,503,1062,2816,5304,16767,27059

%N Indices of primes in sequence defined by A(0) = 41, A(n) = 10*A(n-1) + 51 for n > 0.

%C Numbers n such that (420*10^n - 51)/9 is prime.

%C Numbers n such that digit 4 followed by n >= 0 occurrences of digit 6 followed by digit 1 is prime.

%C Numbers corresponding to terms <= 503 are certified primes.

%C a(20) > 10^5. - _Robert Price_, May 27 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/4/46661.htm#prime">Prime numbers of the form 466...661</a>.

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

%F a(n) = A102994(n) - 1.

%e 461 is prime, hence 1 is a term.

%t Select[Range[0, 1000], PrimeQ[(420*10^# - 51)/9] &] (* _Robert Price_, May 27 2015 *)

%o (PARI) a=41;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a+51)

%o (PARI) for(n=0,1500,if(isprime((420*10^n-51)/9),print1(n,",")))

%Y Cf. A000533, A002275, A102994.

%K nonn,hard,more

%O 1,3

%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(18)-a(19) from Kamada data by _Ray Chandler_, Apr 30 2015

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Last modified June 15 16:13 EDT 2019. Contains 324142 sequences. (Running on oeis4.)