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

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

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: A357996 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