Generate Random numbers only once when spreadsheet is opened

I'm struggling with rand() and randbetween().

This is what I'm looking for:I open my spreadsheet, it generates 20 differents seeds (some between 1 and 12, some between 1 and 6, some between 1 and 3 and some between 1 and 10000) and keep them the same until I close.

When I open again, new numbers are generated and kept the same until I close.Doing manually (Ctrl+C, Ctrl+V) would be a nightmare, because I want to expand in the future to more than 100 different seeds.

A button assigned to a script that automates all the Ctrl+C, Ctrl+V in the beginning could work.

Any ideas?

Thanks!