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Possible Duplicate:
What is the term for a factorial type operation, but with summation instead of products?

Is there a similar function for the addition operator as there is the factorial function for the multiplication operator?

For factorials it is 5! = 5*4*3*2*1, is there a function that would do 5+4+3+2+1?

Thanks,

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    yes, n(n+1)/2 :)2012-06-25

1 Answers 1

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As far as I know we haven't given that expression a name since we may write it explicitly as $ \sum_{i=1}^ni = {n+1 \choose 2} = \frac{n(n+1)}{2}. $

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    mhmm I've see$n$ that notation before somewhere :)2013-08-05