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A101720
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Indices of primes in sequence defined by A(0) = 43, A(n) = 10*A(n-1) - 7 for n > 0.
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0
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0, 3, 8, 9, 30, 69, 159, 170, 276, 629, 723, 3716, 5541, 5633
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Numbers n such that (380*10^n + 7)/9 is prime.
Numbers n such that digit 4 followed by n >= 0 occurrences of digit 2 followed by digit 3 is prime.
Numbers corresponding to terms <= 723 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
| 42223 is prime, hence 3 is a term.
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PROG
| (PARI) a=43; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-7)
(PARI) for(n=0, 1500, if(isprime((380*10^n+7)/9), print1(n, ", ")))
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CROSSREFS
| Cf. A000533, A002275.
a(n) = A102985(n) - 1.
Sequence in context: A099256 A167344 A025615 * A093439 A000927 A055513
Adjacent sequences: A101717 A101718 A101719 * A101721 A101722 A101723
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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 14 2004
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EXTENSIONS
| More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
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