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Re: Bug in Sum?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg119925] Re: Bug in Sum?
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Thu, 30 Jun 2011 06:29:34 -0400 (EDT)
  • Reply-to: hanlonr at cox.net

For a workaround, generalize the problem

Sum[1/(n (1 + n)) 1/((1 - x)^r), {n, 1, M}]

M/((1 - x)^r*(1 + M))

% /. r -> 4

M/((1 + M)*(1 - x)^4)


Bob Hanlon

---- Dario <dario.benedetti at aei.mpg.de> wrote: 

=============
I am very puzzled by the fact that Mathematica does not evaluate the following Sum (it keeps running endlessly):

Sum[1/(n  (1 + n)) 1/((1 - x)^4) , {n, 1, M}]

where x and M are some undefined variables,

but it does evaluate

Sum[1/(n  (1 + n)) 1/((1 - x)^2) , {n, 1, M}]

where I have only changed the power of (1-x), which should not matter as it must factor out!

Any help on this please?




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