The OEIS is supported by the many generous donors to the OEIS Foundation.

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

1

`%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_
`