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%I #6 Sep 03 2013 23:46:22
%S 1,2,3,5,7,11,15,23,47,95
%N f(n), f(f(n)), ... are all prime, where f(n) = (n-1)/2. Stop when f(...f(n)...) is less than 4.
%C There are no more terms since 95 is composite.
%e (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 than 2 exist, end. (47-1)/2=23(prime);(23-1)/2=11(prime); (11-1)/2=5(prime); (5-1)/2=2; no composite numbers smaller than 2 exist, end.
%t 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
%K nonn,easy,fini,full
%O 1,2
%A _Vladimir Joseph Stephan Orlovsky_, Sep 28 2009
%E Corrected and edited by _Charles R Greathouse IV_, Oct 05 2009
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