A101153 - OEIS

%I #14 Jan 17 2019 13:44:06

%S 0,3,17,27,54,1727,1875,1883,6840,10781,25365,98445,137249

%N Indices of primes in sequence defined by A(0) = 79, A(n) = 10*A(n-1) - 1 for n > 0.

%C Numbers n such that (710*10^n + 1)/9 is a prime.

%C Numbers n such that digit 7 followed by n >= 0 occurrences of digit 8 followed by digit 9 is a prime.

%C Numbers corresponding to terms <= 54 are certified primes.

%C The next term after 1883 is greater than 5000. - _Ryan Propper_, Jun 16 2005

%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/7/78889.htm#prime">Prime numbers of the form 788...889</a>.

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

%F a(n) = A103067(n) - 1.

%e 78889 is a prime, hence 3 is a term.

%o (PARI) a=79;for(n=0,1000,if(isprime(a),print1(n,","));a=10*a-1)

%o (PARI) for(n=0,1000,if(isprime((710*10^n+1)/9),print1(n,",")))

%Y Cf. A000533, A002275, A103067.

%K nonn,hard,more

%O 1,2

%A _Klaus Brockhaus_ and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 03 2004

%E 3 more terms from _Ryan Propper_, Jun 16 2005

%E 6840 from Herman Jamke (hermanjamke(AT)fastmail.fm), Apr 28 2007

%E a(10)-a(13) from Kamada data by _Ray Chandler_, Apr 23 2015