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%I #7 Jul 14 2012 11:14:22
%S 14,15,21,28,30,35,39,42,45,46,51,55,56,57,60,63,65,66,75,77,78,84,85,
%T 87,90,91,92,93,94,95,98,102,110,111,112,114,117,119,120,123,126,130,
%U 132,135,141,143,145,147,150,153,154,155,156,158,168,170,171,174,175
%N Becomes prime after exactly 2 iterations of f(x) = sum of prime factors of x.
%C f(x) = sum of prime factors without multiplicity, so that f(1500) = 2+3+5 = 10.
%t i2Q[n_]:=PrimeQ[NestList[Total[Transpose[FactorInteger[#]][[1]]]&,n,2]] == {False,False,True}; Select[Range[200],i2Q] (* _Harvey P. Dale_, Jul 14 2012 *)
%K nonn
%O 1,1
%A _David W. Wilson_
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