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MathGroup Archive 2002

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The prime factors of n.

  • To: mathgroup at
  • Subject: [mg32673] The prime factors of n.
  • From: "Robert G. Wilson v" <rgwv at>
  • Date: Wed, 6 Feb 2002 03:41:24 -0500 (EST)
  • Sender: owner-wri-mathgroup at

Hello all,

        I wish to receive a list of prime factors of n not in the form
returned by FactorInteger. Instead I want only the primes the number of
times they appear. As an example I will use 72. FactorInteger[72] gives
{ {2,3}, {3,2} }. I wish the list would read { 2, 2, 2, 3, 3 }. Is the
following the best that I can do? f[n_Integer] := Module[{a =
FactorInteger[n], b = {}}, While[Length[a] > 0, Do[b = Append[b, a[[1,
1]]], {a[[1, 2]]}]; a = Drop[a, 1]]; b] .


Sincerely yours,

Robert G. "Bob" Wilson, V

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