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%I #7 Aug 18 2013 09:57:59
%S 62,69,124,133,190,194,201,206,207,213,217,219,226,235,238,248,249,
%T 254,282,286,303,309,310,314,355,380,386,388,406,411,412,426,447,451,
%U 452,458,469,476,483,489,496,505,508,553,564,572,598,602,603,606,620,621
%N Becomes prime after exactly 4 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.
%H Harvey P. Dale, <a href="/A047823/b047823.txt">Table of n, a(n) for n = 1..1000</a>
%t p4iQ[n_]:=PrimeQ[NestList[Total[Transpose[FactorInteger[#]][[1]]]&, n,4]] == {False,False,False,False,True}; Select[Range[700],p4iQ] (* _Harvey P. Dale_, Aug 18 2013 *)
%K nonn
%O 1,1
%A _David W. Wilson_
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