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A101722
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Indices of primes in sequence defined by A(0) = 49, A(n) = 10*A(n-1) - 61 for n > 0.
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1
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OFFSET
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1,1
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COMMENTS
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Numbers n such that (380*10^n + 61)/9 is prime.
Numbers n such that digit 4 followed by n >= 0 occurrences of digit 2 followed by digit 9 is prime.
Some of the larger entries may only correspond to probable primes.
Certified primality of number corresponding to term 2042 using Primo. - Ryan Propper, Jun 23 2005
a(5) > 10^5. - Robert Price, May 08 2015
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REFERENCES
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Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
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LINKS
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Table of n, a(n) for n=1..4.
Makoto Kamada, Prime numbers of the form 422...229.
Index entries for primes involving repunits.
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FORMULA
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a(n) = A102987(n+1) - 1.
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EXAMPLE
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4229 is prime, hence 2 is a term.
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MATHEMATICA
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Select[Range[0, 3000], PrimeQ[(380*10^# + 61)/9] &] (* Robert Price, May 08 2015 *)
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PROG
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(PARI) a=49; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-61)
(PARI) for(n=0, 1500, if(isprime((380*10^n+61)/9), print1(n, ", ")))
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CROSSREFS
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Cf. A000533, A002275, A102987.
Sequence in context: A124361 A166339 A024034 * A004908 A275002 A004813
Adjacent sequences: A101719 A101720 A101721 * A101723 A101724 A101725
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KEYWORD
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nonn,bref,hard,more
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AUTHOR
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Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 14 2004
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EXTENSIONS
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More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Apr 28 2007
a(4) from Kamada link by Ray Chandler, Apr 24 2015
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STATUS
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approved
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