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A101075
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Indices of primes in sequence defined by A(0) = 89, A(n) = 10*A(n-1) - 21 for n > 0.
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0
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0, 2, 16, 18, 32, 38, 168, 452, 610, 882, 1472, 6510, 9646
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Numbers n such that (780*10^n + 21)/9 is prime.
Numbers n such that digit 8 followed by n >= 0 occurrences of digit 6 followed by digit 9 is prime.
Numbers corresponding to terms <= 882 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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EXAMPLE
| 8669 is prime, hence 2 is a term.
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PROG
| (PARI) a=89; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-21)
(PARI) for(n=0, 1500, if(isprime((780*10^n+21)/9), print1(n, ", ")))
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CROSSREFS
| Cf. A000533, A002275.
a(n) = A103088(n) - 1.
Sequence in context: A004831 A180923 A058242 * A022370 A161802 A050850
Adjacent sequences: A101072 A101073 A101074 * A101076 A101077 A101078
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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
| More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
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