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A056266
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Indices of primes in sequence defined by A(0) = 99, A(n) = 10*A(n-1) - 1 for n > 0.
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2
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5, 71, 95, 113, 203, 983, 1225, 4793, 20719, 133579, 411589
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OFFSET
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1,1
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COMMENTS
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Numbers n such that (890*10^n + 1)/9 is prime.
Numbers n such that the number 9 8(n times) 9 is prime.
Numbers corresponding to terms <= 983 are certified primes. For numbers greater than 4793, 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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9888889 is prime, hence 5 is a term.
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MATHEMATICA
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Select[Range[2000], PrimeQ[(890 10^# + 1) / 9] &] (* Vincenzo Librandi, Nov 02 2014 *)
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PROG
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(PARI) a=99; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-1)
(PARI) for(n=0, 1500, if(isprime((890*10^n+1)/9), print1(n, ", ")))
(Magma) [n: n in [0..1000] | IsPrime((890*10^n+1) div 9)]; // Vincenzo Librandi, Nov 02 2014
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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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Additional comments from Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Nov 27 2004
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
Two more terms from PDP table added and comments section edited by Patrick De Geest, Nov 02 2014
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STATUS
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approved
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