5:10 ah, my favourite prime test "sounds prime" haha! I have to admit that's exactly what I was thinking as you said it. I love that little simplification at the end where you recognised the 3 sets of the same digits! It makes sense given its multiplied by 101, but I am pretty sure I'd have entirely missed that.
Everybody knows it’s a well tested tried and true method for prime testing. It definitely went through my head that I was happy I spotted the 101 multiples as well! For some reason a number like 20200 doesn’t look like a multiple of 101, but obviously it is.
I had no idea how to approach this at first, but as soon as you wrote down N = 2,020 + 10,000 k, it became clear and I was able to find the answer. Nice one!
