The second folding thickness is 0.2 * 2 = 0.1* 2 * 2 = 0.1* 22 = 0.4.

The third folding thickness is 0.4 * 2 = 0. 1 * 2 3 = 0.8.

By analogy, the thickness of the 20th floor is 0.1* 220 =104857.6mm =10485.76cm =104.8576m..

I.e. approximately equal to 35 layers.