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A128509
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Initial prime, greater than 7, of a prime chain of length n under the iteration x -> 2x-7.
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1
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11, 13, 13, 367, 4987, 9697, 78007, 13356127, 13356127, 6753069187, 218617084627, 35679817649197, 92975416840027
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OFFSET
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1,1
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COMMENTS
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From the definition we see that the sequence is monotonic (but not strictly) increasing. The sequence is a generalized Cunningham chain. - Stefan Steinerberger, May 12 2007
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LINKS
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EXAMPLE
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a(2) = 13 because 13, 13*2-7=19 and 19*2-7=31 are primes.
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MATHEMATICA
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k = 5; For[n = 2, n <= 10, n++, While[Union[PrimeQ[NestList[2# - 7 &, Prime[k], n]], PrimeQ[NestList[2# - 7 &, Prime[k], n]]] != {True}, k++ ]; Print[Prime[k]]] (* Stefan Steinerberger, May 12 2007 *)
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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