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Re: Finding a formula for a sum

• To: mathgroup at smc.vnet.net
• Subject: [mg35134] Re: Finding a formula for a sum
• From: Samuel Kutter <sk256 at phy.cam.ac.uk>
• Date: Tue, 25 Jun 2002 19:55:12 -0400 (EDT)
• Organization: University of Cambridge, England
• References: <af97ij$2t$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

Hello

I don't know how to guess sum-formulae by using mathematica given a series
of integer numbers, but I would recommend using Mozilla and go to:

http://www.research.att.com/~njas/sequences/index.html

Sam

On Tue, 25 Jun 2002 Matthias.Bode at oppenheim.de wrote:

> Dear Colleagues,
> 
> when trying to find the number of diagonals in a convex polygon (all corners
> on the perimeter of a circle) with n corners I came across that sum:
> 
> +(n-3) ; up to here = diagonals in a triangle.
> 
> +(n-3) ; up to here = diagonals in a quadrangle.
> 
> +(n-4) ; up to here = diagonals in a pentagon.
> 
> +(n-5) ; up to here = diagonals in a hexagon.
> 
> +(n-6) ; up to here = diagonals in a heptagon.
> and so on.
> 
> I found the general formula (n*n -3*n)/2 with pencil and paper.
> 
> How could I coax MATHEMATICA into helping me to find the generalization in
> this case - and of course for more difficult ones as well?
>