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A101738
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Indices of primes in sequence defined by A(0) = 41, A(n) = 10*A(n-1) + 81 for n > 0.
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0
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0, 1, 3, 6, 23, 171, 172, 217, 438, 2562, 2781, 2879, 3714, 4391, 10819, 14591
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,3
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COMMENTS
| Numbers n such that (450*10^n - 81)/9 is prime.
Numbers n such that digit 4 followed by n >= 0 occurrences of digit 9 followed by digit 1 is prime.
Numbers corresponding to terms <= 438 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
| 49991 is prime, hence 3 is a term.
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PROG
| (PARI) a=41; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+81)
(PARI) for(n=0, 1500, if(isprime((450*10^n-81)/9), print1(n, ", ")))
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CROSSREFS
| Cf. A000533, A002275.
a(n) = A103001(n) - 1.
Sequence in context: A013211 A013212 A013218 * A083525 A106213 A129520
Adjacent sequences: A101735 A101736 A101737 * A101739 A101740 A101741
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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 01 2008
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