[Σ Sigma notation](https://www.khanacademy.org/math/ap-calculus-ab/ab-integration-new/ab-6-3/v/sigma-notation-sum)
Sum of some terms
Sum of the first 10 #'s

```
-------
 10   |                                        |
 Σ  i | 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 | 55
 i=1  |                                        |
-------

-------
 100  |
 Σ  i | 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 .... 100
 i=1  |
-------

sum := 0
for i = 1; i <= 100; i++ {
  sum += i
}

```

The summation is an arithmetic series and has the value
```
-------
 n    |                  |
 Σ  k | 1 + 2 + ... + n  |
 k=1  |                  |
-------
```

Sum of squares:
```
-------
 n      |    n(n+1)(2n+1)
 Σ  k^2 | = --------------
 k=0    |         6
-------

-------
 n      |    n^2(n+1)^2
 Σ  k^3 | = -------------
 k=0    |        4
-------
```