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A056255 Indices of primes in sequence defined by A(0) = 33, A(n) = 10*A(n-1) + 43 for n > 0.

%I A056255 #25 Jan 17 2019 13:44:05
%S A056255 1,13,53,67,83,85,155,2765,3379,3875,5207,10745,15767,31315,40957,
%T A056255 45803,46565,51007,80161
%N A056255 Indices of primes in sequence defined by A(0) = 33, A(n) = 10*A(n-1) + 43 for n > 0.
%C A056255 Numbers n such that (340*10^n - 43)/9 is prime.
%C A056255 Numbers n such that digit 3 followed by n >= 0 occurrences of digit 7 followed by digit 3 is prime.
%C A056255 Numbers corresponding to terms <= 5207 are certified primes.
%D A056255 Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
%H A056255 Patrick De Geest, <a href="http://www.worldofnumbers.com/deplat.htm#pdp373">PDP Reference Table - 373</a>.
%H A056255 Makoto Kamada, <a href="https://stdkmd.net/nrr/3/37773.htm#prime">Prime numbers of the form 377...773</a>.
%H A056255 <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F A056255 a(n) = A082708(n) - 2.
%e A056255 373 is prime, hence 1 is a term.
%t A056255 Select[Range[0, 2000], PrimeQ[(340 10^# - 43) / 9] &] (* _Vincenzo Librandi_, Nov 03 2014 *)
%o A056255 (PARI) a=33;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a+43)
%o A056255 (PARI) for(n=0,1500,if(isprime((340*10^n-43)/9),print1(n,",")))
%Y A056255 Cf. A000533, A002275, A082708.
%K A056255 nonn,hard,more
%O A056255 1,2
%A A056255 _Robert G. Wilson v_, Aug 18 2000
%E A056255 Additional comments from _Klaus Brockhaus_ and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 20 2004
%E A056255 Edited by _N. J. A. Sloane_ at the suggestion of _Andrew S. Plewe_, Jun 15 2007
%E A056255 More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
%E A056255 Two more terms from PDP table and a link added, and comments section updated, by _Patrick De Geest_, Nov 02 2014
%E A056255 Edited by _Ray Chandler_, Nov 05 2014