%I
%S 26,33,38,52,70,74,76,86,99,104,105,106,115,122,129,138,140,146,148,
%T 152,159,161,166,172,178,185,187,195,205,208,209,212,218,221,222,230,
%U 231,244,246,266,267,276,278,280,292,296,297,302,304,305,315,321,327
%N Becomes prime after exactly 3 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 aQ[n_] := Length[NestWhileList[Plus @@ First /@ FactorInteger[#] &, n, ! PrimeQ[#] &]] == 4; Select[Range[2, 330], aQ] (* _Jayanta Basu_, Aug 10 2013 *)
%K nonn
%O 1,1
%A _David W. Wilson_
