I have the following function:

```
f(n) = f(n - 1) + (n - 1)
f(0) = 0
n >= 0
```

I have `n`

declared on column A, and need the result of `f(n)`

on column B.

I'm trying to find the Excel formula equivalent for this function.

Sample Result:

```
A | B
--+--
0 | 0
```

or:

```
A | B
--+--
1 | 0
```

or:

```
A | B
--+--
4 | 6
```

**but never**:

```
A | B
--+--
0 | 0
1 | 0
2 | 1
...
```

The biggest problem is, I can't simulate the value of `f(n - 1)`

. So referencing the previous row like the above example is invalid. I'm almost sure the answer is trivial, I just can't find it.