### replicate recursive sum

i have a function defined ~~as: (cant post links or images so ill put the latex code)~~as

```
\begin{align
```*}
f(0) &= 1\\
f(n) &= 1 + \sum_{j=0}^{n-1}f(j) \text{ for every } n > 0
\end{align*}

` `

https ://imgur.com/a/SfF2Edl.png

how can i replicate this function in sagemath using the sum function? i know it can be done in pure python with recursion but then whats the point of sagemath and symbolic calculation?

what ive tried so far is:

```
f(x) = 1 if x == 0 else sum(1+f(j-1), j, 0, x-1)
```

but i get the following error:

```
NameError: name 'f' is not defined
```

now i know its not possible to use recursion on a variable like this but there must be some tricky way to go about doing that (i hope so and thats why im here)

thanks in advance