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MathGroup Archive 2006

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sum of binomials .. bug ?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg70486] sum of binomials .. bug ?
  • From: yann_che2 at yahoo.fr
  • Date: Tue, 17 Oct 2006 02:59:50 -0400 (EDT)

Hi everyone,

on Mathematica 5.2 (mac os x), experimenting sums of binomials, i tried
the following:

In[6]:=   f[k_] := Sum[Binomial[21 - k, i], {i, 0, 10 - k}]
In[7]:=   x = 3; f[x]
Out[7]:= 63004
In[8]:=   Clear[x] ; f[x] /. x -> 3
Out[8]:= 262144
In[9]:=   Clear[x] ; f[x]
Out[9]:= 2^(21-x)


does anyone know why Out[7] and Out[8] give different results ? do you
think it is a bug ? i searched everywhere in the forums but couldn't
find anything that helped.
do you have a clue ?

yann


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