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A102021
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Indices of primes in sequence defined by A(0) = 19, A(n) = 10*A(n-1) - 31 for n > 0.
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0
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0, 2, 3, 6, 11, 50, 86, 122, 197, 201, 536, 830, 1322, 2507, 2630, 5567, 6896, 7523, 9938
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Numbers n such that (140*10^n + 31)/9 is prime.
Numbers n such that digit 1 followed by n >= 0 occurrences of digit 5 followed by digit 9 is prime.
Numbers corresponding to terms <= 830 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
| 1559 is prime, hence 2 is a term.
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PROG
| (PARI) a=19; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-31)
(PARI) for(n=0, 1500, if(isprime((140*10^n+31)/9), print1(n, ", ")))
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CROSSREFS
| Cf. A000533, A002275.
a(n) = A102938(n) - 1.
Sequence in context: A022490 A102952 A065653 * A144641 A082002 A102779
Adjacent sequences: A102018 A102019 A102020 * A102022 A102023 A102024
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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 28 2004
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EXTENSIONS
| More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
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