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 A056258 Indices of primes in sequence defined by A(0) = 77, A(n) = 10*A(n-1) - 23 for n > 0. 2
 9, 29, 119, 483, 1485, 1577, 13671, 13809, 15093, 72771, 94211 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Numbers n such that (670*10^n + 23)/9 is prime. Numbers n such that digit 7 followed by n >= 0 occurrences of digit 4 followed by digit 7 is prime. Numbers corresponding to terms <= 1577 are certified primes. For larger numbers see P. De Geest, PDP Reference Table. REFERENCES Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467. LINKS Patrick De Geest, PDP Reference Table - 747. Makoto Kamada, Prime numbers of the form 744...447. FORMULA a(n) = A082712(n) - 2. EXAMPLE 74444444447 is prime, hence 9 is a term. MATHEMATICA Select[Range[0, 2000], PrimeQ[(670 10^# + 23) / 9] &] (* Vincenzo Librandi, Nov 03 2014 *) PROG (PARI) a=77; for(n=0, 1600, if(isprime(a), print1(n, ", ")); a=10*a-23) (PARI) for(n=0, 1600, if(isprime((670*10^n+23)/9), print1(n, ", "))) CROSSREFS Cf. A000533, A002275, A082712. Sequence in context: A288744 A183245 A101141 * A147282 A146602 A146413 Adjacent sequences:  A056255 A056256 A056257 * A056259 A056260 A056261 KEYWORD nonn,hard,more AUTHOR Robert G. Wilson v, Aug 18 2000 EXTENSIONS Edited by Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 03 2004 More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008 Two more terms added from PDP table 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 July 20 12:37 EDT 2018. Contains 312804 sequences. (Running on oeis4.)