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A056254 Indices of primes in sequence defined by A(0) = 33, A(n) = 10*A(n-1) + 23 for n > 0.

%I A056254 #24 Jan 17 2019 13:44:05
%S A056254 1,7,139,229,425,461,725,1973,7229,45859,47303
%N A056254 Indices of primes in sequence defined by A(0) = 33, A(n) = 10*A(n-1) + 23 for n > 0.
%C A056254 Numbers n such that (320*10^n - 23)/9 is prime.
%C A056254 Numbers n such that digit 3 followed by n >= 0 occurrences of digit 5 followed by digit 3 is prime.
%C A056254 Numbers corresponding to terms <= 1973 are certified primes. For larger numbers see P. De Geest, PDP Reference Table.
%D A056254 Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
%H A056254 Patrick De Geest, <a href="http://www.worldofnumbers.com/deplat.htm#pdp353">PDP Reference Table - 353</a>.
%H A056254 Makoto Kamada, <a href="https://stdkmd.net/nrr/3/35553.htm#prime">Prime numbers of the form 355...553</a>.
%H A056254 <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F A056254 a(n) = A082707(n) - 2.
%e A056254 353 is prime, hence 1 is a term.
%t A056254 Select[Range[0, 2000], PrimeQ[(320 10^# - 23) / 9] &] (* _Vincenzo Librandi_, Nov 03 2014 *)
%o A056254 (PARI) a=33;for(n=0,2000,if(isprime(a),print1(n,","));a=10*a+23)
%o A056254 (PARI) for(n=0,2000,if(isprime((320*10^n-23)/9),print1(n,",")))
%Y A056254 Cf. A000533, A002275, A082707.
%K A056254 nonn,hard
%O A056254 1,2
%A A056254 _Robert G. Wilson v_, Aug 18 2000
%E A056254 Additional comments from _Klaus Brockhaus_ and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 20 2004
%E A056254 Edited by _N. J. A. Sloane_ at the suggestion of _Andrew S. Plewe_, May 31 2007, Jun 15 2007
%E A056254 More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
%E A056254 Comments section and a link updated by _Patrick De Geest_, Nov 02 2014
%E A056254 Edited by _Ray Chandler_, Nov 05 2014