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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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified October 2 20:53 EDT 2022. Contains 357230 sequences. (Running on oeis4.)