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A047825 Becomes prime after exactly 6 iterations of f(x) = sum of prime factors of x. 1
393, 889, 1142, 1179, 1257, 1270, 1285, 1315, 1389, 1502, 1542, 1563, 1578, 1838, 2217, 2284, 2305, 2326, 2474, 2540, 2761, 2766, 2787, 2827, 2913, 3004, 3084, 3156, 3193, 3207, 3505, 3507, 3537, 3589, 3676, 3771, 3826, 3873, 3957, 4006, 4167, 4195 (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..2500

MATHEMATICA

bp6Q[n_]:=Length[NestWhileList[Total[FactorInteger[#][[All, 1]]]&, n, CompositeQ[ #]&]]==7; Select[Range[4200], bp6Q] (* Harvey P. Dale, Aug 01 2021 *)

CROSSREFS

Sequence in context: A256742 A158002 A083752 * A227942 A201815 A201554

Adjacent sequences:  A047822 A047823 A047824 * A047826 A047827 A047828

KEYWORD

nonn

AUTHOR

David W. Wilson

STATUS

approved

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Last modified September 25 03:12 EDT 2022. Contains 356953 sequences. (Running on oeis4.)