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A101153
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Indices of primes in sequence defined by A(0) = 79, A(n) = 10*A(n-1) - 1 for n > 0.
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2
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0, 3, 17, 27, 54, 1727, 1875, 1883, 6840, 10781, 25365, 98445, 137249
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OFFSET
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1,2
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COMMENTS
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Numbers n such that (710*10^n + 1)/9 is a prime.
Numbers n such that digit 7 followed by n >= 0 occurrences of digit 8 followed by digit 9 is a prime.
Numbers corresponding to terms <= 54 are certified primes.
The next term after 1883 is greater than 5000. - Ryan Propper, Jun 16 2005
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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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78889 is a prime, hence 3 is a term.
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PROG
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(PARI) a=79; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a-1)
(PARI) for(n=0, 1000, if(isprime((710*10^n+1)/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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Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 03 2004
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EXTENSIONS
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6840 from Herman Jamke (hermanjamke(AT)fastmail.fm), Apr 28 2007
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STATUS
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approved
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