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A101542
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Indices of primes in sequence defined by A(0) = 67, A(n) = 10*A(n-1) + 27 for n > 0.
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1
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0, 2, 3, 5, 9, 19, 50, 137, 189, 359, 377, 392, 1383, 1593, 2758, 2867, 5394, 7493, 10490, 11198, 12189, 33593, 38255, 89168, 165915
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OFFSET
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1,2
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COMMENTS
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Numbers n such that (630*10^n - 27)/9 is prime.
Numbers n such that digit 6 followed by n >= 0 occurrences of digit 9 followed by digit 7 is prime.
Numbers corresponding to terms <= 392 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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6997 is prime, hence 2 is a term.
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MATHEMATICA
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Select[Range[0, 200000], PrimeQ[(630*10^# - 27)/9] &] (* Robert Price, Aug 17 2015 *)
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PROG
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(PARI) a=67; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+27)
(PARI) for(n=0, 1500, if(isprime((630*10^n-27)/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 06 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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