Re: The prime factors of n.

*To*: mathgroup at smc.vnet.net*Subject*: [mg32729] Re: The prime factors of n.*From*: lalu_bhatt at yahoo.com (Bhuvanesh)*Date*: Thu, 7 Feb 2002 05:10:31 -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: > 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 Well, here's a simple alternate way that is clearer for me: In[1]:= f[n_Integer] := Flatten[Map[Table[#[[1]], {#[[2]]}]&, FactorInteger[n]]] In[2]:= f[72] Out[2]= {2, 2, 2, 3, 3} -- Bhuvanesh, Wolfram Research.