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A101010
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Indices of primes in sequence defined by A(0) = 93, A(n) = 10*A(n-1) + 23 for n > 0.
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1
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OFFSET
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1,2
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COMMENTS
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Numbers n such that (860*10^n - 23)/9 is prime.
Numbers n such that digit 9 followed by n >= 0 occurrences of digit 5 followed by digit 3 is prime.
Numbers corresponding to terms <= 328 are certified primes.
a(8) > 10^5. - Robert Price, Nov 08 2015
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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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Table of n, a(n) for n=1..7.
Makoto Kamada, Prime numbers of the form 955...553.
Index entries for primes involving repunits.
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FORMULA
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a(n) = A103101(n+1) - 1.
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EXAMPLE
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953 is prime, hence 1 is a term.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[(860*10^# - 23)/9] &] (* Robert Price, Nov 08 2015 *)
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PROG
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(PARI) a=93; for(n=0, 2000, if(isprime(a), print1(n, ", ")); a=10*a+23)
(PARI) for(n=0, 2000, if(isprime((860*10^n-23)/9), print1(n, ", ")))
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CROSSREFS
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Cf. A000533, A002275, A103101.
Sequence in context: A054658 A023296 A139948 * A201854 A195460 A195461
Adjacent sequences: A101007 A101008 A101009 * A101011 A101012 A101013
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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 27 2004
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EXTENSIONS
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a(7) from Kamada data by Ray Chandler, Apr 28 2015
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STATUS
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approved
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