Re: The prime factors of n.

*To*: mathgroup at smc.vnet.net*Subject*: [mg32759] Re: The prime factors of n.*From*: "Steve Durbin" <steved at vale.demon.co.uk>*Date*: Fri, 8 Feb 2002 03:49:35 -0500 (EST)*References*: <a3qqjj$27t$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

"Robert G. Wilson v" <rgwv at kspaint.com> wrote in message news:a3qqjj$27t$1 at smc.vnet.net... > 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] . This is probably not the best way, but it at least avoids the iterator and list altering operations: In[367]:= superfactorinteger[x_Integer] := Module[{z, y}, z = FactorInteger[x]; q[y : {_, _}] := Table[y[[1]], {y[[2]]}]; Flatten[Map[q, z]]]; In[368]:= superfactorinteger[1] superfactorinteger[72] superfactorinteger[10101] Out[368]= {} Out[369]= {2, 2, 2, 3, 3} Out[370]= {3, 7, 13, 37} Cheers, -- Steve Durbin | Look! Minimalism comes to ASCII art! | .