At 18:22 21/06/2013 -0500, Dale Erwin wrote:
I realize that a variable can take any value, but some mathematical functions limit the possible values.
Oh, indeed!
... I thought this particular function was stated as Sigma 1 to n = n*(n + 1) / 2 (where n > 1).
It also works for n = 1, so n >= 1 is probably better.
You don't really have a series if n is not > 1.
Indeed: the original question asked to include numbers (i.e., in this case, integers) from 1 up to n. You can't really count up from 1 to 0, or to any fractional value, or to negative values.
If you did allow the series to run backward (from 1 to 0) you would get Sigma 1 to 0 = 0 * 1 / 2 which evaluates to 0.
Depending on how you defined your function, you could choose to include that as a permitted result. Apparently that's what the questioner wants.
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