

A047830


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


0



2, 4, 14, 26, 62, 134, 393, 1774, 13682, 41037, 167073, 334142, 4677862, 14033577, 79464886, 476789307, 3488435822, 34884358195
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OFFSET

0,1


COMMENTS

f(x) = sum of prime factors without multiplicity, so that f(1500) = 2+3+5 = 10.
a(18) <= 148005789513. a(19) <= 1603226096774. a(20) <= 16032260967715.  Donovan Johnson


LINKS

Table of n, a(n) for n=0..17.


MATHEMATICA

k = 2; Table[While[Length[NestWhileList[Plus @@ First /@ FactorInteger[#] &, k, ! PrimeQ[#] &]] != i + 1, k++]; k, {i, 0, 12}] (* Jayanta Basu, Aug 10 2013 *)


CROSSREFS

Sequence in context: A102930 A135113 A050564 * A036051 A115626 A116021
Adjacent sequences: A047827 A047828 A047829 * A047831 A047832 A047833


KEYWORD

nonn


AUTHOR

David W. Wilson


EXTENSIONS

a(14)a(15) from Donovan Johnson, Oct 13 2009
Edited comment and a(16)a(17) from Donovan Johnson, Oct 16 2010


STATUS

approved



