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A101075
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Indices of primes in sequence defined by A(0) = 89, A(n) = 10*A(n-1) - 21 for n > 0.
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1
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0, 2, 16, 18, 32, 38, 168, 452, 610, 882, 1472, 6510, 9646, 21592, 39990, 40156
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OFFSET
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1,2
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COMMENTS
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Numbers n such that (780*10^n + 21)/9 is prime.
Numbers n such that digit 8 followed by n >= 0 occurrences of digit 6 followed by digit 9 is prime.
Numbers corresponding to terms <= 882 are certified primes.
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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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8669 is prime, hence 2 is a term.
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MATHEMATICA
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Flatten[Position[NestList[10#-21&, 89, 9700], _?PrimeQ]]-1 (* Harvey P. Dale, May 26 2012 *)
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PROG
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(PARI) a=89; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-21)
(PARI) for(n=0, 1500, if(isprime((780*10^n+21)/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), Nov 30 2004
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EXTENSIONS
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More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
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STATUS
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approved
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