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 A101739 Indices of primes in sequence defined by A(0) = 43, A(n) = 10*A(n-1) + 63 for n > 0. 2

%I

%S 0,2,3,7,13,15,23,60,79,86,103,107,143,2156,3324,4121,20717,51162,

%T 140743

%N Indices of primes in sequence defined by A(0) = 43, A(n) = 10*A(n-1) + 63 for n > 0.

%C Numbers n such that (450*10^n - 63)/9 is prime.

%C Numbers n such that digit 4 followed by n >= 0 occurrences of digit 9 followed by digit 3 is prime.

%C Numbers corresponding to terms <= 143 are certified primes.

%C a(20) > 2*10^5. - _Robert Price_, Sep 15 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/4/49993.htm#prime">Prime numbers of the form 499...993</a>.

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

%F a(n) = A103002(n) - 1.

%e 4993 is prime, hence 2 is a term.

%t Select[Range[0, 100000], PrimeQ[(450*10^# - 63)/9] &] (* _Robert Price_, Sep 15 2015 *)

%o (PARI) a=43;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a+63)

%o (PARI) for(n=0,1500,if(isprime((450*10^n-63)/9),print1(n,",")))

%Y Cf. A000533, A002275, A108837, A103002.

%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 01 2008

%E a(17)-a(18) from Kamada data by _Ray Chandler_, May 01 2015

%E a(19) from _Robert Price_, Sep 15 2015

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Last modified May 25 11:27 EDT 2020. Contains 334592 sequences. (Running on oeis4.)