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MathGroup Archive 2002

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Reciprocal Sums

  • To: mathgroup at smc.vnet.net
  • Subject: [mg32472] Reciprocal Sums
  • From: "Juan" <erfa11 at hotmail.com>
  • Date: Tue, 22 Jan 2002 03:19:57 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

Hello,
I need your help to resolve this question (I give a example for n=12):

In[1]:= << DiscreteMath`Combinatorica`

In[2]:= n = 12;

In[3]:= p = Partitions[n];


Now, I want to get from p thouse partitions which reciprocal sum is a 
integer.

In[4]:= r = Cases[p, x_ /; IntegerQ[Plus @@ (1/x)]]

Out[4]:= {{6, 3, 2, 1}, {4, 4, 2, 1, 1}, {3, 3, 3, 1, 1, 1}, {2, 2, 2, 2, 2, 
2}, {2, 2,2, 2, 1, 1, 1, 1}, {2, 2, 1, 1, 1, 1, 1, 1, 1, 1}, {1, 1, 1, 1, 1, 
1, 1, 1, 1, 1, 1, 1}}

But, is n is a big number, then you have to wait a big number of seconds to 
get r.

Any suggestion to do that better-faster?

Best regard
Juan


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