A snippet from Marcus du Sautoy's The Number Mysteries, Chapter 3, in the section called HOW GOOD ARE YOU AT RANDOMNESS is shown below. My question is, why does the author use superscripts instead of subscripts here?

A snippet from Marcus du Sautoy's The Number Mysteries, Chapter 3, in the section called HOW GOOD ARE YOU AT RANDOMNESS is shown below. My question is, why does the author use superscripts instead of subscripts here?

I used subscripts in the UK edition but the US edition seems to have flipped it to a superscript. Superscripts of course have a different meaning so it is definitely a bad choice. Thanks for pointing this out.