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 A101732 Indices of primes in sequence defined by A(0) = 41, A(n) = 10*A(n-1) + 61 for n > 0. 1

%I

%S 0,21,924,2339,15954,16097,55511,82751

%N Indices of primes in sequence defined by A(0) = 41, A(n) = 10*A(n-1) + 61 for n > 0.

%C Numbers n such that (430*10^n - 61)/9 is prime.

%C Numbers n such that digit 4 followed by n >= 0 occurrences of digit 7 followed by digit 1 is prime.

%C Numbers corresponding to terms <= 924 are certified primes.

%C a(9) > 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/4/47771.htm#prime">Prime numbers of the form 477...771</a>.

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

%F a(n) = A102995(n) - 1.

%e 47 is prime, hence 0 is a term.

%t Select[Range[0, 1000], PrimeQ[(430*10^# - 61)/9] &] (* _Robert Price_, Jun 01 2015 *)

%o (PARI) a=41;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a+61)

%o (PARI) for(n=0,1500,if(isprime((430*10^n-61)/9),print1(n,",")))

%Y Cf. A000533, A002275, A102995.

%K nonn,hard,more

%O 1,2

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

%E a(5)-a(6) from Kamada data by _Ray Chandler_, May 01 2015

%E a(7)-a(8) from _Robert Price_, Jun 01 2015

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Last modified October 23 22:42 EDT 2019. Contains 328378 sequences. (Running on oeis4.)