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Search: id:A165801
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| A165801 |
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f(n), f(f(n)), ... are all prime, where f(n) = (n-1)/2. Stop when f(...f(n)...) is less than 4. |
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+0
5
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OFFSET
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1,2
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COMMENT
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There are no more terms since 95 is composite.
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EXAMPLE
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(95-1)/2=47(prime); (47-1)/2=23(prime); (23-1)/2=11(prime); (11-1)/2=5(prime); (5-1)/2=2(prime); no composite numbers smaller then 2 exists,end. (47-1)/2=23(prime);(23-1)/2=11(prime); (11-1)/2=5(prime); (5-1)/2=2;no composite numbers smaller then 2 exists,end.
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MATHEMATICA
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f[n_]:=Module[{k=n}, While[k>3, k=(k-1)/2; If[ !PrimeQ[k], Break[]]]; PrimeQ[k]]; lst={}; Do[If[f[n], AppendTo[lst, n]], {n, 5!}]; lst
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CROSSREFS
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Sequence in context: A024792 A055771 A052955 this_sequence A022480 A024791 A118084
Adjacent sequences: A165798 A165799 A165800 this_sequence A165802 A165803 A165804
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KEYWORD
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nonn,easy,fini,full
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AUTHOR
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Vladimir Orlovsky (4vladimir(AT)gmail.com), Sep 28 2009
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EXTENSIONS
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Corrected and edited by Charles R Greathouse IV (charles.greathouse(AT)case.edu), Oct 05 2009
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