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MathGroup Archive 2002

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Re: The prime factors of n.

  • To: mathgroup at smc.vnet.net
  • Subject: [mg32727] Re: [mg32673] The prime factors of n.
  • From: Chris Johnson <cjohnson at shell.faradic.net>
  • Date: Thu, 7 Feb 2002 05:10:24 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

One solution would be...

factorIntegerList[n_] := Flatten[PadLeft[{}, #2, #1] & @@@
FactorInteger[n]]

(@@@ Is a function of newer versions of Mathematica.  It represents Apply
at level spec {1})

Chris

On Wed, 6 Feb 2002, Robert G. Wilson v wrote:

> 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] .
> 
> See
> http://www.research.att.com/cgi-bin/access.cgi/as/njas/sequences/eisA.cgi?Anum=037276
> 
> Sincerely yours,
> 
> Robert G. "Bob" Wilson, V
> 
> 



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