1 | initial version |

Note that you can use `(1 .. 20)`

to iterate through the integers from 1 to 20,
without constructing the list of these integers, as `[1 .. 20]`

does.

To obtain an iterator of squares:

```
sage: (k^2 for k in (1 .. 20))
```

To obtain the list of squares:

```
sage: [k^2 for k in (1 .. 20)]
```

To obtain the sum of squares:

```
sage: sum(k^2 for k in (1 .. 20))
```

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