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A100997
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Indices of primes in sequence defined by A(0) = 91, A(n) = 10*A(n-1) - 9 for n > 0.
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0
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2, 3, 4, 8, 21, 26, 35, 56, 61, 77, 200, 536, 695, 789, 904, 1037, 66885
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| Numbers n such that 90*10^n + 1 is prime.
Numbers n such that digit 9 followed by n >= 0 occurrences of digit 0 followed by digit 1 is prime.
Numbers corresponding to terms <= 1037 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
| 900001 is prime, hence 4 is a term.
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PROG
| (PARI) a=91; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-9)
(PARI) for(n=0, 1500, if(isprime(90*10^n+1), print1(n, ", ")))
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CROSSREFS
| Cf. A000533, A002275.
a(n) = A056797(n) - 1.
Sequence in context: A105055 A108506 A129284 * A128657 A091930 A124526
Adjacent sequences: A100994 A100995 A100996 * A100998 A100999 A101000
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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), Nov 26 2004
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EXTENSIONS
| 66885 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
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