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A101823
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Indices of primes in sequence defined by A(0) = 31, A(n) = 10*A(n-1) - 9 for n > 0.
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0
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0, 2, 6, 9, 27, 35, 66, 80, 146, 482, 642, 1019, 1899, 2619, 10452, 27719, 52823
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Numbers n such that 30*10^n + 1 is prime.
Numbers n such that digit 3 followed by n >= 0 occurrences of digit 0 followed by digit 1 is prime.
Numbers corresponding to terms <= 642 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
| 3001 is prime, hence 2 is a term.
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PROG
| (PARI) a=31; for(n=0, 2000, if(isprime(a), print1(n, ", ")); a=10*a-9)
(PARI) for(n=0, 2000, if(isprime(30*10^n+1), print1(n, ", ")))
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CROSSREFS
| Cf. A000533, A002275, A100499.
a(n) = A056807(n) - 1.
Sequence in context: A205875 A121624 A103019 * A093397 A082459 A129831
Adjacent sequences: A101820 A101821 A101822 * A101824 A101825 A101826
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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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