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A101070
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Indices of primes in sequence defined by A(0) = 81, A(n) = 10*A(n-1) + 41 for n > 0.
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0
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OFFSET
| 1,1
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COMMENTS
| Numbers n such that (770*10^n - 41)/9 is prime.
Numbers n such that digit 8 followed by n >= 0 occurrences of digit 5 followed by digit 1 is prime.
Numbers corresponding to terms <= 470 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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FORMULA
| a(n) = A103083(n) - 1. - Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
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EXAMPLE
| 8555555555555555555551 is prime, hence 20 is a term.
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PROG
| (PARI) a=81; for(n=0, 1200, if(isprime(a), print1(n, ", ")); a=10*a+41)
(PARI) for(n=0, 1200, if(isprime((770*10^n-41)/9), print1(n, ", ")))
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CROSSREFS
| Cf. A000533, A002275.
Sequence in context: A167306 A061840 A067065 * A070717 A114813 A069827
Adjacent sequences: A101067 A101068 A101069 * A101071 A101072 A101073
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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 30 2004
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EXTENSIONS
| One more term from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
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