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Search: id:A057331
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| A057331 |
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a(n) = smallest prime p such that the first n iterates of p under x->2x+1 are all primes. |
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+0
20
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| 2, 2, 2, 2, 2, 89, 1122659, 19099919, 85864769, 26089808579, 554688278429, 4090932431513069
(list; graph; listen)
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OFFSET
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0,1
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COMMENT
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Initial terms of A000040, A005384, A007700, A023272, A023302, A023330.
For n>10 a(n) == -1 (mod 2*3*5*11*13). - Farideh Firoozbakht (mymontain(AT)yahoo.com), Apr 24 2004
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LINKS
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C. K. Caldwell, Latest results about Cunningham Chains
Index entries for sequences related to primes in arithmetic progressions
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EXAMPLE
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a(5) = 89 because the numbers 89, 179, 359, 719, 1439, 2879 are all primes and 89 is the first number to have this property.
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MATHEMATICA
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f[n_] := 2n + 1; k = 1; Do[ While[ Union[ PrimeQ[ NestList[ f, Prime[k], n]]] != {True}, k++ ]; Print[ Prime[k]], {n, 1, 9} ]
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CROSSREFS
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See also A005602.
Adjacent sequences: A057328 A057329 A057330 this_sequence A057332 A057333 A057334
Sequence in context: A060359 A029665 A056993 this_sequence A067089 A090872 A063473
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KEYWORD
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nonn,nice
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AUTHOR
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Patrick De Geest (pdg(AT)worldofnumbers.com), Aug 15 2000.
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EXTENSIONS
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More terms from Farideh Firoozbakht (mymontain(AT)yahoo.com), Apr 24 2004
a(13) (from the Caldwell link) sent by Peter Deleu, Hulste, Belgium, Nov 22, 2004
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