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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
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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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FORMULA
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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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KEYWORD
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nonn,hard,more
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AUTHOR
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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
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STATUS
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approved
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