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A101847
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Indices of primes in sequence defined by A(0) = 39, A(n) = 10*A(n-1) - 1 for n > 0.
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0
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1, 2, 5, 16, 19, 44, 56, 77, 118, 136, 508, 709, 1126, 1517, 1760, 3085, 3146, 9925
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Numbers n such that (350*10^n + 1)/9 is prime.
Numbers n such that digit 3 followed by n >= 0 occurrences of digit 8 followed by digit 9 is prime.
Numbers corresponding to terms <= 709 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
| 3889 is prime, hence 2 is a term.
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PROG
| (PARI) a=39; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-1)
(PARI) for(n=0, 1500, if(isprime((350*10^n+1)/9), print1(n, ", ")))
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CROSSREFS
| Cf. A000533, A002275.
a(n) = A102980(n) - 1.
Sequence in context: A111790 A127580 A098048 * A117557 A175735 A137997
Adjacent sequences: A101844 A101845 A101846 * A101848 A101849 A101850
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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), Dec 20 2004
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EXTENSIONS
| More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
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