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A047828 Becomes prime after exactly 9 iterations of f(x) = sum of prime factors of x. 1
41037, 55694, 82083, 86662, 88982, 90177, 106221, 106562, 109838, 111388, 123111, 134098, 168049, 173324, 177697, 177964, 179995, 195458, 207574, 213124, 214779, 215994, 219676, 222776, 229315, 233857, 240070, 240115, 244534, 246249 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

f(x) = sum of prime factors without multiplicity, so that f(1500) = 2+3+5 = 10.

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..5000

MATHEMATICA

spf9Q[n_]:=Module[{spf=TakeDrop[NestList[Total[FactorInteger[#][[All, 1]]]&, n, 9], 9]}, AllTrue[spf[[1]], !PrimeQ[#]&]&&PrimeQ[spf][[2, 1]]]; Select[ Range[ 250000], spf9Q] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Apr 20 2017 *)

CROSSREFS

Sequence in context: A133863 A033532 A173361 * A141711 A074379 A237395

Adjacent sequences:  A047825 A047826 A047827 * A047829 A047830 A047831

KEYWORD

nonn

AUTHOR

David W. Wilson

STATUS

approved

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Last modified August 4 21:32 EDT 2021. Contains 346455 sequences. (Running on oeis4.)