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A101571
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Indices of primes in sequence defined by A(0) = 57, A(n) = 10*A(n-1) - 53 for n > 0.
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1
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OFFSET
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1,1
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COMMENTS
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Numbers n such that (460*10^n + 53)/9 is prime.
Numbers n such that digit 5 followed by n >= 0 occurrences of digit 1 followed by digit 7 is prime.
Numbers corresponding to terms <= 52 are certified primes. No further terms up to 2400.
a(5) > 10^5. - Robert Price, Jun 20 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..4.
Makoto Kamada, Prime numbers of the form 511...117.
Index entries for primes involving repunits.
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FORMULA
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a(n) = A103006(n+1) - 1.
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EXAMPLE
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511111111111111111111117 is prime, hence 22 is a term.
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PROG
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(PARI) a=57; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a-53)
(PARI) for(n=0, 1000, if(isprime((460*10^n+53)/9), print1(n, ", ")))
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CROSSREFS
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Cf. A000533, A002275, A103006.
Sequence in context: A111576 A277979 A177726 * A290381 A122502 A244212
Adjacent sequences: A101568 A101569 A101570 * A101572 A101573 A101574
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KEYWORD
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nonn,more
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AUTHOR
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Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 09 2004
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EXTENSIONS
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a(3)-a(4) from Kamada data by Ray Chandler, Apr 30 2015
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STATUS
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approved
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