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Search: id:A101525
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| A101525 |
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Indices of primes in sequence defined by A(0) = 61, A(n) = 10*A(n-1) + 21 for n > 0. |
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+0
1
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| 0, 1, 3, 6, 17, 18, 22, 23, 33, 40, 55, 63, 83, 148, 271, 754, 1271, 2397, 2685, 4799, 5197, 6216, 8736
(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 (570*10^n - 21)/9 is prime.
Numbers n such that digit 6 followed by n >= 0 occurrences of digit 3 followed by digit 1 is prime.
Numbers corresponding to terms <= 754 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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631 is prime, hence 1 is a term.
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PROGRAM
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(PARI) a=61; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+21)
(PARI) for(n=0, 1500, if(isprime((570*10^n-21)/9), print1(n, ", ")))
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CROSSREFS
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Cf. A000533, A002275.
a(n) = A103032(n) - 1.
Adjacent sequences: A101522 A101523 A101524 this_sequence A101526 A101527 A101528
Sequence in context: A028405 A014645 A036050 this_sequence A139476 A063618 A024823
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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 06 2004
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EXTENSIONS
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More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
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