I've watched the first part and the whole approach seems odd to me.

How many times in your life have you *thought* about a 20 digit number? I can't hold a 20-digit number in my head. It would have to be something written down, and as it's bigger than most calculators it would have to be in an exceptional context, eg some book making a point about some large number, or a very long multiplication on paper. Even saying I've seen 100 20-digit numbers in my lifetime feels like a massive overestimate.

Many of the 117 billion people who have ever lived (number from the video) would have not had the notation to have even considered a 20-digit number, but let's suppose given the average lifespan in the past, that on average every person that ever lived has "thought" of 50 20-digit numbers.

Even if those 50 numbers were unique to each person, that means humanity has covered around 6 x 10^12 of the 20-digit numbers. There are 9 x 10^19 20-digit numbers, so humanity has at best covered 0.000007% of them. I'm absolutely confident that if I write down a 20-digit number now, no-one will have ever thought of it.

It's clear I could go for something less than 20-digits and still be very confident.