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A165802
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Primes p with f(p), f(f(p)), ... all prime, where f(n) = (n-1)/2. Stop when f(...f(p)...) is less than 4.
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2
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OFFSET
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1,1
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LINKS
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Table of n, a(n) for n=1..7.
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EXAMPLE
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(47-1)/2=23(prime);(23-1)/2=11(prime); (11-1)/2=5(prime); (5-1)/2=2.
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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[p=Prime[n]; If[f[p], AppendTo[lst, p]], {n, 5!}]; lst
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CROSSREFS
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Subsequence of A165801.
Sequence in context: A252791 A068148 A036344 * A107798 A119660 A079148
Adjacent sequences: A165799 A165800 A165801 * A165803 A165804 A165805
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KEYWORD
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nonn,fini,full
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AUTHOR
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Vladimir Joseph Stephan Orlovsky, Sep 28 2009
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EXTENSIONS
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Edited by Charles R Greathouse IV, Oct 05 2009
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STATUS
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approved
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