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A056246
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Indices of primes in sequence defined by A(0) = 11, A(n) = 10*A(n-1) + 41 for n > 0.
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2
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OFFSET
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1,3
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COMMENTS
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Numbers n such that (140*10^n - 41)/9 is a prime.
Numbers n such that digit 1 followed by n >= 0 occurrences of digit 5 followed by digit 1 is a prime.
Numbers corresponding to terms <= 561 are certified primes.
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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..9.
Patrick De Geest, PDP Reference Table - 151.
Makoto Kamada, Prime numbers of the form 155...551.
Index entries for primes involving repunits.
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FORMULA
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a(n) = A082699(n-1) - 2 for n > 1.
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EXAMPLE
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151 is a prime, hence 1 is a term.
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MATHEMATICA
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Select[Range[0, 2000], PrimeQ[(140 10^# - 41) / 9] &] (* Vincenzo Librandi, Nov 03 2014 *)
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PROG
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(PARI) a=11; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+41)
(PARI) for(n=0, 1500, if(isprime((140*10^n-41)/9), print1(n, ", ")))
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CROSSREFS
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Cf. A000533, A002275, A068646, A082699.
Sequence in context: A269414 A162307 A128069 * A360081 A061427 A069516
Adjacent sequences: A056243 A056244 A056245 * A056247 A056248 A056249
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KEYWORD
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nonn,hard
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AUTHOR
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Robert G. Wilson v, Aug 18 2000
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EXTENSIONS
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Additional comments from Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 28 2004
Edited by N. J. A. Sloane, Jun 15 2007
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
Added and updated a link, by Patrick De Geest, Nov 02 2014
Edited by Ray Chandler, Nov 04 2014
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STATUS
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approved
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