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Search: id:A101154
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| A101154 |
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Indices of primes in sequence defined by A(0) = 71, A(n) = 10*A(n-1) + 81 for n > 0. |
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+0
1
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| 0, 4, 10, 11, 16, 27, 45, 47, 60, 72, 137, 177, 212, 404, 761, 1052, 1156, 1426, 2864, 3147, 3614
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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Numbers n such that (720*10^n - 81)/9 is prime.
Numbers n such that digit 7 followed by n >= 0 occurrences of digit 9 followed by digit 1 is prime.
Numbers corresponding to terms <= 761 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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799991 is prime, hence 4 is a term.
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PROGRAM
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(PARI) a=71; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+81)
(PARI) for(n=0, 1500, if(isprime((720*10^n-81)/9), print1(n, ", ")))
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CROSSREFS
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Cf. A000533, A002275.
a(n) = A103068(n) - 1.
Adjacent sequences: A101151 A101152 A101153 this_sequence A101155 A101156 A101157
Sequence in context: A074226 A106631 A120261 this_sequence A090070 A078005 A092428
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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 03 2004
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EXTENSIONS
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a(19) from Mohammed Bouayoun (Mohammed.Bouayoun(AT)sanef.com), Apr 13 2006
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
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