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A101057
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Indices of primes in sequence defined by A(0) = 89, A(n) = 10*A(n-1) - 81 for n > 0.
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0
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0, 1, 2, 5, 11, 19, 20, 36, 41, 54, 59, 97, 99, 103, 222, 236, 259, 500, 569, 599, 697, 8856
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,3
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COMMENTS
| Numbers n such that 80*10^n + 9 is prime.
Numbers n such that digit 8 followed by n >= 0 occurrences of digit 0 followed by digit 9 is prime.
Numbers corresponding to terms <= 697 are certified primes.
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REFERENCES
| Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
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LINKS
| Makoto Kamada, Factorizations of near-repdigit numbers.
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FORMULA
| a(n) = A103070(n) - 1. - 8856 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
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EXAMPLE
| 8000009 is prime, hence 5 is a term.
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PROG
| (PARI) a=89; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a-81)
(PARI) for(n=0, 1000, if(isprime(80*10^n + 9), print1(n, ", ")))
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CROSSREFS
| Cf. A000533, A002275.
Sequence in context: A025200 A132455 A132459 * A045362 A157978 A045363
Adjacent sequences: A101054 A101055 A101056 * A101058 A101059 A101060
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KEYWORD
| nonn,hard,more
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AUTHOR
| Klaus Brockhaus (klaus-brockhaus(AT)t-online.de) and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Nov 30 2004
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EXTENSIONS
| 8856 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
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