A047827 - OEIS

A047827

Becomes prime after exactly 8 iterations of f(x) = sum of prime factors of x.

%I #10 Nov 22 2012 12:45:00

%S 13682,18002,19137,22934,24014,24787,27364,27849,30062,30993,32577,

%T 33477,35410,35798,36004,36398,36706,39206,43333,43917,44493,45219,

%U 45734,45868,46142,46405,48028,49546,50642,51295,52413,53283,54728

%N Becomes prime after exactly 8 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.

%H Harvey P. Dale, <a href="/A047827/b047827.txt">Table of n, a(n) for n = 1..3000</a>

%t pa8iQ[n_]:=PrimeQ/@NestList[Total[Transpose[FactorInteger[#]][[1]]]&, n, 8] == {False,False,False,False,False,False,False,False,True}; Select[Range[ 55000], pa8iQ] (* _Harvey P. Dale_, Nov 22 2012 *)

%K nonn

%O 1,1

%A _David W. Wilson_