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Search: id:A102031
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| A102031 |
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Indices of primes in sequence defined by A(0) = 19, A(n) = 10*A(n-1) - 1 for n > 0. |
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1
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OFFSET
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1,2
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COMMENT
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Numbers n such that (170*10^n + 1)/9 is prime.
Numbers n such that digit 1 followed by n >= 0 occurrences of digit 8 followed by digit 9 is prime.
Numbers corresponding to terms <= 842 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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EXAMPLE
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1889 is prime, hence 2 is a term.
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PROGRAM
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(PARI) a=19; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-1)
(PARI) for(n=0, 1500, if(isprime((170*10^n+1)/9), print1(n, ", ")))
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CROSSREFS
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Cf. A000533, A002275.
a(n) = A102945(n) - 1.
Sequence in context: A042805 A134096 A132571 this_sequence A072386 A015180 A145512
Adjacent sequences: A102028 A102029 A102030 this_sequence A102032 A102033 A102034
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KEYWORD
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nonn,hard,more
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AUTHOR
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Klaus Brockhaus (klaus-brockhaus(AT)t-online.de) and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 28 2004
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EXTENSIONS
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6299 from Herman Jamke (hermanjamke(AT)fastmail.fm), Dec 22 2007
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