cp's OEIS Frontend

A101078 Indices of primes in sequence defined by A(0) = 89, A(n) = 10*A(n-1) - 11 for n > 0.

%I A101078 #15 Jan 17 2019 13:44:06
%S A101078 0,2,5,30,35,60,116,228,338,3164,3957,5276,5342,6078,6534,8484,15083,
%T A101078 34536
%N A101078 Indices of primes in sequence defined by A(0) = 89, A(n) = 10*A(n-1) - 11 for n > 0.
%C A101078 Numbers n such that (790*10^n + 11)/9 is prime.
%C A101078 Numbers n such that digit 8 followed by n >= 0 occurrences of digit 7 followed by digit 9 is prime.
%C A101078 Numbers corresponding to terms <= 338 are certified primes.
%C A101078 a(19) > 10^5. - _Robert Price_, Oct 27 2015
%D A101078 Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
%H A101078 Makoto Kamada, <a href="https://stdkmd.net/nrr/8/87779.htm#prime">Prime numbers of the form 877...779</a>.
%H A101078 <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F A101078 a(n) = A103091(n) - 1.
%e A101078 8777779 is prime, hence 5 is a term.
%t A101078 Select[Range[0, 100000], PrimeQ[(790*10^# + 11)/9] &] (* _Robert Price_, Oct 27 2015 *)
%o A101078 (PARI) a=89;for(n=0,1000,if(isprime(a),print1(n,","));a=10*a-11)
%o A101078 (PARI) for(n=0,1000,if(isprime((790*10^n+11)/9),print1(n,",")))
%Y A101078 Cf. A000533, A002275, A103091.
%K A101078 nonn,hard,more
%O A101078 1,2
%A A101078 _Klaus Brockhaus_ and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Nov 30 2004
%E A101078 More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
%E A101078 a(17)-a(18) from Kamada data by _Ray Chandler_, Apr 29 2015