# Sigma Notation

This symbol (called Sigma) means "sum up" |

I love Sigma, it is fun to use, and can do many clever things.

So | means to sum things up ... |

## Sum What? |
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Sum whatever appears after the Sigma: |
so we sum |
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## But What is the Value of n |
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The values are shown below |
it says |
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## OK, Let's Go ... |
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So now we add up 1,2,3 and 4: |

Here it is in one diagram:

## More Powerful

But Σ can do more powerful things than that!

You could square *n* each time and sum the result:

You could "add up the first four terms in the sequence **2n+1**":

And you don't have to use *n*. Here we use i and sum up i × (i+1), going from **1** to **3**:

And you can start and end with any number. Here we go from **3** to **5**:

Try some of your own with the Sigma Calculator.

And now you get the idea, you might like to read the more advanced topic Partial Sums.

## Why is it called "Sigma"

Sigma is the upper case letter |