Number system that provides alternative to real numbers (mentioned by 3Blue1Brown), wha't the name?

Question

https://youtu.be/U_lKUK2MCsg?t=171

Grant Sanderson (3Blue1Brown channel) (auto-generated subtitles):

I think the way that we extend to the real numbers there's a little bit of choice in that so there's this funny number system called the serial numbers

I've tried googling serial/sereal/servial/sevial number system but found only modern codes to identify staff.

https://en.wikipedia.org/wiki/List_of_numeral_systems is rather long and Grant had not given much detail what to look for even if it's there. What's the system he mentioned properly called? Any good links to read about? TIA

Answer 1

Sanderson said “surreal numbers”.

Like Jamie Radcliffe, I also suggest Conway's On Numbers and Games and Knuth's Surreal Numbers.

Answer 2

You’re looking for the surreal numbers. They appear in Conway’s “On Numbers and Games” and a book by Knuth, quite lighthearted, called “Surreal Numbers”.

Answer 3

https://en.m.wikipedia.org/wiki/P-adic_number And there’s a nice video by veritasium on youtube