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%I #17 Jan 17 2019 13:44:07
%S 0,1,4,6,18,19,27,57,249,396,7590,32715,70977,83586
%N Indices of primes in sequence defined by A(0) = 17, A(n) = 10*A(n-1) - 13 for n > 0.
%C Numbers n such that (140*10^n + 13)/9 is prime.
%C Numbers n such that digit 1 followed by n >= 0 occurrences of digit 5 followed by digit 7 is prime.
%C Numbers corresponding to terms <= 396 are certified primes.
%C a(15) > 10^5. - _Robert Price_, Jan 17 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/1/15557.htm#prime">Prime numbers of the form 155...557</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A102937(n+1) - 1.
%e 157 is prime, hence 1 is a term.
%o (PARI) a=17;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a-13)
%o (PARI) for(n=0,1500,if(isprime((140*10^n+13)/9),print1(n,",")))
%Y Cf. A000533, A002275, A102937.
%K nonn,hard,more
%O 1,3
%A _Klaus Brockhaus_ and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 28 2004
%E 7590 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
%E a(12)-a(14) derived from A102937 by _Robert Price_, Jan 17 2015
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