The OEIS is supported by the many generous donors to the OEIS Foundation.
Reminder: The OEIS is hiring a new managing editor, and the application deadline is January 26.
Reminder: The OEIS is hiring a new managing editor, and the application deadline is January 26.
%I #14 Jan 17 2019 13:44:07
%S 0,2,3,6,11,50,86,122,197,201,536,830,1322,2507,2630,5567,6896,7523,
%T 9938,10673,11616,13256,14370,20175,36554,36873,40130,43124,58728,
%U 97043
%N Indices of primes in sequence defined by A(0) = 19, A(n) = 10*A(n-1) - 31 for n > 0.
%C Numbers n such that (140*10^n + 31)/9 is prime.
%C Numbers n such that digit 1 followed by n >= 0 occurrences of digit 5 followed by digit 9 is prime.
%C Numbers corresponding to terms <= 830 are certified primes.
%C a(31) > 10^5. _Robert Price_, Feb 03 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/1/15559.htm#prime">Prime numbers of the form 155...559</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A102938(n) - 1.
%e 1559 is prime, hence 2 is a term.
%o (PARI) a=19;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a-31)
%o (PARI) for(n=0,1500,if(isprime((140*10^n+31)/9),print1(n,",")))
%Y Cf. A000533, A002275, A102938.
%K nonn,hard,more
%O 1,2
%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(20)-a(30) from _Robert Price_, Feb 03 2015