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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. 1
 1, 13, 53, 67, 83, 85, 155, 2765, 3379, 3875, 5207, 10745, 15767, 31315, 40957, 45803, 46565, 51007, 80161 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Numbers n such that (340*10^n - 43)/9 is prime. Numbers n such that digit 3 followed by n >= 0 occurrences of digit 7 followed by digit 3 is prime. Numbers corresponding to terms <= 5207 are certified primes. REFERENCES Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467. LINKS Patrick De Geest, PDP Reference Table - 373. Makoto Kamada, Prime numbers of the form 377...773. FORMULA a(n) = A082708(n) - 2. EXAMPLE 373 is prime, hence 1 is a term. MATHEMATICA Select[Range[0, 2000], PrimeQ[(340 10^# - 43) / 9] &] (* Vincenzo Librandi, Nov 03 2014 *) PROG (PARI) a=33; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+43) (PARI) for(n=0, 1500, if(isprime((340*10^n-43)/9), print1(n, ", "))) CROSSREFS Cf. A000533, A002275, A082708. Sequence in context: A317467 A076163 A207977 * A141885 A262447 A165352 Adjacent sequences:  A056252 A056253 A056254 * A056256 A056257 A056258 KEYWORD nonn,hard,more,changed AUTHOR Robert G. Wilson v, Aug 18 2000 EXTENSIONS Additional comments from Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 20 2004 Edited by N. J. A. Sloane at the suggestion of Andrew S. Plewe, Jun 15 2007 More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008 Two more terms from PDP table and a link added, and comments section updated, by Patrick De Geest, Nov 02 2014 Edited by Ray Chandler, Nov 05 2014 STATUS approved

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Last modified January 18 04:47 EST 2019. Contains 319269 sequences. (Running on oeis4.)