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incorrect Sum[]

  • To: mathgroup at
  • Subject: [mg107571] incorrect Sum[]
  • From: David Bevan <david.bevan at>
  • Date: Wed, 17 Feb 2010 08:03:48 -0500 (EST)

Sum[] gets the following sum wrong:

In[]:= f[n_,k_]:=-((2 (-1)^k n Pochhammer[1-2 n,-1+k])/k!)

Note that f[n,k] is actually the same as Binomial[2n,k].

In[]:= Sum[f[n,k],{k,0,n}]
Out[]= 4^n

In[]:= Sum[f[n,k]/.n->5,{k,0,5}]
Out[]= 638
Out[]= {1,10,45,120,210,252}
Out[]= 638

In[]:= 4^5
Out[]= 1024

It gets the following correct:

In[]:= Sum[f[n,k],{k,0,2n}]
Out[]= 4^n

I've forwarded this to submitabug.

David %^>

David Bevan
Development Manager
Pitney Bowes Emtex Software
Tel: +44 (0)1923 279300
David.Bevan at

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