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 A047830 Least number which becomes prime after exactly n iterations of f(x) = sum of prime factors of x. 0

%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

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Last modified December 3 07:15 EST 2022. Contains 358512 sequences. (Running on oeis4.)