Hi again Dan. Question about this formula you wrote. I don’t understand the notation.

```
sum(k -> loops(n,k), 1:n) == factorial(n)
```

What does `sum(k->loops(n,k), 1:n)`

mean? Is something ranging from `k`

to `loops(n,k)`

? Also, what is this `1:n`

for?

Thanks again.

`sum`

iterates over a collection, applies a function to each element, and sums the results from the function. `k->loops(n,k)`

is an anonymous function of `k`

that returns `loops(n,k)`

. `1:n`

is a range, and is the collection that `sum`

iterates. The result here is `loops(n,1) + loops(n,2) + ... + loops(n,n)`

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