cp's OEIS Frontend

A101973 Indices of primes in sequence defined by A(0) = 23, A(n) = 10*A(n-1) + 63 for n > 0.

%I A101973 #19 Jan 17 2019 13:44:06
%S A101973 0,1,4,9,28,38,113,483,864,4179,5384,13121,13831,22675,25019,30056,
%T A101973 35909,37934,42294,50193,110075,184123,191151
%N A101973 Indices of primes in sequence defined by A(0) = 23, A(n) = 10*A(n-1) + 63 for n > 0.
%C A101973 Numbers n such that (270*10^n - 63)/9 is prime.
%C A101973 Numbers n such that digit 2 followed by n >= 0 occurrences of digit 9 followed by digit 3 is prime.
%C A101973 Numbers corresponding to terms <= 864 are certified primes.
%C A101973 a(21) > 10^5. - Robert Price, Jan 25 2015
%C A101973 a(24) > 2*10^5. - Robert Price, Aug 09 2015
%D A101973 Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
%H A101973 Makoto Kamada, <a href="https://stdkmd.net/nrr/2/29993.htm#prime">Prime numbers of the form 299...993</a>.
%H A101973 <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F A101973 a(n) = A102964(n) - 1.
%e A101973 293 is prime, hence 1 is a term.
%t A101973 Select[Range[0, 200000], PrimeQ[(270*10^# - 63)/9] &] (* _Robert Price_, Aug 09 2015 *)
%o A101973 (PARI) a=23;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a+63)
%o A101973 (PARI) for(n=0,1500,if(isprime((270*10^n-63)/9),print1(n,",")))
%Y A101973 Cf. A000533, A002275, A102964.
%K A101973 nonn,hard,more
%O A101973 1,3
%A A101973 _Klaus Brockhaus_ and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 23 2004
%E A101973 More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
%E A101973 a(12)-a(20) derived from A102964 by _Robert Price_, Jan 25 2015
%E A101973 a(21)-a(23) derived from A102964 by _Robert Price_, Aug 09 2015