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Search: id:A101721
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| A101721 |
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Indices of primes in sequence defined by A(0) = 47, A(n) = 10*A(n-1) - 43 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 (380*10^n + 43)/9 is prime.
Numbers n such that digit 4 followed by n >= 0 occurrences of digit 2 followed by digit 7 is prime.
Numbers corresponding to terms <= 324 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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Makoto Kamada, Factorizations of near-repdigit numbers.
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EXAMPLE
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42227 is prime, hence 3 is a term.
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PROGRAM
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(PARI) a=47; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-43)
(PARI) for(n=0, 1500, if(isprime((380*10^n+43)/9), print1(n, ", ")))
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CROSSREFS
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Cf. A000533, A002275.
a(n) = A102986(n) - 1.
Sequence in context: A152435 A157086 A051376 this_sequence A065973 A110973 A136411
Adjacent sequences: A101718 A101719 A101720 this_sequence A101722 A101723 A101724
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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 14 2004
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EXTENSIONS
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More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
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