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Search: id:A102020
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| A102020 |
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Indices of primes in sequence defined by A(0) = 17, A(n) = 10*A(n-1) - 13 for n > 0. |
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+0
1
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| 0, 1, 4, 6, 18, 19, 27, 57, 249, 396, 7590
(list; graph; listen)
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OFFSET
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1,3
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COMMENT
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Numbers n such that (140*10^n + 13)/9 is prime.
Numbers n such that digit 1 followed by n >= 0 occurrences of digit 5 followed by digit 7 is prime.
Numbers corresponding to terms <= 396 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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157 is prime, hence 1 is a term.
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PROGRAM
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(PARI) a=17; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-13)
(PARI) for(n=0, 1500, if(isprime((140*10^n+13)/9), print1(n, ", ")))
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CROSSREFS
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Cf. A000533, A002275.
a(n) = A102937(n) - 1.
Sequence in context: A061361 A113610 A062046 this_sequence A125133 A109310 A120391
Adjacent sequences: A102017 A102018 A102019 this_sequence A102021 A102022 A102023
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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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7590 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
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