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A056258
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Indices of primes in sequence defined by A(0) = 77, A(n) = 10*A(n-1) - 23 for n > 0.
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2
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9, 29, 119, 483, 1485, 1577, 13671, 13809, 15093, 72771, 94211
(list;
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history;
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internal format)
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OFFSET
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1,1
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COMMENTS
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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.
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REFERENCES
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Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
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LINKS
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Table of n, a(n) for n=1..11.
Patrick De Geest, PDP Reference Table - 747.
Makoto Kamada, Prime numbers of the form 744...447.
Index entries for primes involving repunits.
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FORMULA
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a(n) = A082712(n) - 2.
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EXAMPLE
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74444444447 is prime, hence 9 is a term.
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MATHEMATICA
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Select[Range[0, 2000], PrimeQ[(670 10^# + 23) / 9] &] (* Vincenzo Librandi, Nov 03 2014 *)
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PROG
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(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, ", ")))
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CROSSREFS
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Cf. A000533, A002275, A082712.
Sequence in context: A288744 A183245 A101141 * A147282 A146602 A146413
Adjacent sequences: A056255 A056256 A056257 * A056259 A056260 A056261
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KEYWORD
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nonn,hard,more
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AUTHOR
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Robert G. Wilson v, Aug 18 2000
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EXTENSIONS
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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
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STATUS
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approved
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