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A101066
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Indices of primes in sequence defined by A(0) = 81, A(n) = 10*A(n-1) + 31 for n > 0.
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0
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25, 35, 37, 59, 79, 91, 173, 485, 626, 998, 1613, 4381, 4897, 8441
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| Numbers n such that (760*10^n - 31)/9 is prime.
Numbers n such that digit 8 followed by n >= 0 occurrences of digit 4 followed by digit 1 is prime.
Numbers corresponding to terms <= 626 are certified primes.
Next term after 4897 is greater than 10000. - Ryan Propper (rpropper(AT)stanford.edu), Jun 20 2005
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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) = A103079(n) - 1. - Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
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EXAMPLE
| 844444444444444444444444441 is prime, hence 25 is a term.
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PROG
| (PARI) a=81; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a+31)
(PARI) for(n=0, 1000, if(isprime((760*10^n-31)/9), print1(n, ", ")))
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CROSSREFS
| Cf. A000533, A002275.
Sequence in context: A020258 A188059 A098368 * A061442 A049514 A049518
Adjacent sequences: A101063 A101064 A101065 * A101067 A101068 A101069
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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
| Three additional terms, corresponding to probable primes, from Ryan Propper (rpropper(AT)stanford.edu), Jun 20 2005
One more term from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
Edited by T. D. Noe (noe(AT)sspectra.com), Oct 30 2008
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