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%I #23 Jan 04 2021 06:24:43
%S 0,5,10,12,18,22,66,107,117,175,672,779,1087,1218,1655,6244,10738,
%T 12589,17512,25999,32543,53273
%N Indices of primes in sequence defined by A(0) = 31, A(n) = 10*A(n-1) + 51 for n > 0.
%C Numbers n such that (330*10^n - 51)/9 is prime.
%C Numbers n such that digit 3 followed by n >= 0 occurrences of digit 6 followed by digit 1 is prime.
%C a(23) > 10^5. - _Robert Price_, Jan 29 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/3/36661.htm#prime">Prime numbers of the form 366...661</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A102974(n) - 1. [adapted by _Georg Fischer_, Jan 04 2021]
%e 3666661 is prime, hence 5 is a term.
%o (PARI) a=31;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a+51)
%o (PARI) for(n=0,1500,if(isprime((330*10^n-51)/9),print1(n,",")))
%Y Cf. A000533, A002275, A102974.
%K nonn,hard,more
%O 1,2
%A _Klaus Brockhaus_ and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 20 2004
%E More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
%E a(17)-a(22) derived from A102974 by _Robert Price_, Jan 29 2015
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