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MathGroup Archive 2002

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Re: The prime factors of n.

  • To: mathgroup at smc.vnet.net
  • Subject: [mg32732] Re: [mg32673] The prime factors of n.
  • From: Tomas Garza <tgarza01 at prodigy.net.mx>
  • Date: Thu, 7 Feb 2002 05:10:40 -0500 (EST)
  • References: <200202060841.DAA02157@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

In[1]:=
Flatten[(Table[#1[[1]], {#1[[2]]}] & ) /@
   FactorInteger[72]]
Out[1]=
{2, 2, 2, 3, 3}

Tomas Garza
Mexico City

----- Original Message -----
From: "Robert G. Wilson v" <rgwv at kspaint.com>
To: mathgroup at smc.vnet.net
Subject: [mg32732] [mg32673] The prime factors of n.


> 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?An
um=037276
>
> Sincerely yours,
>
> Robert G. "Bob" Wilson, V
>
>



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