Maths Youtuber Noel Friedrich recently made a video about A4 paper[0]. It turns out that since the ISO specification rounds the side lengths down to whole millimeters, with compounding errors, more than 2^10 A10s (smallest paper size in the standard) fit into one A0 (largest size in the standard).

[0] https://www.youtube.com/watch?v=zDKBCIMkDbw