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%I #22 Feb 01 2023 18:19:13
%S 0,1,3,6,9,12,13,21,22,28,37,49,52,66,103,349,375,411,1204,1834,2509,
%T 2667,6096,8295,14295,43368,127348,142033
%N Indices of primes in sequence defined by A(0) = 19, A(n) = 10*A(n-1) - 51 for n > 0.
%C Numbers n such that (120*10^n + 51)/9 is prime.
%C Numbers n such that digit 1 followed by n >= 0 occurrences of digit 3 followed by digit 9 is prime.
%C Numbers corresponding to terms <= 411 are certified primes.
%C a(27) > 10^5. - _Robert Price_, Nov 15 2014
%C a(29) > 2*10^5. - _Tyler Busby_, Feb 01 2023
%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/1/13339.htm#prime">Prime numbers of the form 133...339</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A102933(n) - 1. - _Robert Price_, Nov 15 2014
%e 139 is prime, hence 1 is a term.
%p A102014:=n->`if`(isprime((120*10^n + 51)/9), n, NULL): seq(A102014(n), n=0..1000); # _Wesley Ivan Hurt_, Nov 15 2014
%o (PARI) a=19;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a-51)
%o (PARI) for(n=0,1500,if(isprime((120*10^n+51)/9),print1(n,",")))
%Y Cf. A000533, A002275, A102933.
%K nonn,hard,more
%O 1,3
%A _Klaus Brockhaus_ and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 28 2004
%E More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
%E a(25)-a(26) derived from A102933 by _Robert Price_, Nov 15 2014
%E a(27)-a(28) from _Tyler Busby_, Feb 01 2023
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