How to change max number of VBA function

Hello I wrote a custom function in excel,

but when I use large numbers (250,000) it comes back as #=NUM!

Only relevant info I found seems to be here:
https://support.microsoft.com/en-us/office/how-to-correct-a-num-error-f5193bfc-4400-43f4-88c4-8e1dcca0428b

Yet I have absolutely no idea how or where to do that. 
Clicking on "show calculations steps" just shows me this.

I tried changing from an INTEGER to a DOUBLE, but 250,000 should clearly fit inside of an integer.. so im really confused