%I
%S 2,4,14,26,62,134,393,1774,13682,41037,167073,334142,4677862,14033577,
%T 79464886,476789307,3488435822,34884358195
%N Least number which becomes prime after exactly n 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.
%C a(18) <= 148005789513. a(19) <= 1603226096774. a(20) <= 16032260967715.  Donovan Johnson
%t k = 2; Table[While[Length[NestWhileList[Plus @@ First /@ FactorInteger[#] &, k, ! PrimeQ[#] &]] != i + 1, k++]; k, {i, 0, 12}] (* _Jayanta Basu_, Aug 10 2013 *)
%K nonn
%O 0,1
%A _David W. Wilson_
%E a(14)a(15) from _Donovan Johnson_, Oct 13 2009
%E Edited comment and a(16)a(17) from _Donovan Johnson_, Oct 16 2010
