Interesting, I found this link that looks like a promising starting point: https://artofmemory.com/wiki/Mnemonic_Peg_System/#:~:text=A%....

I found the best ones turned numbers into phonetics, which created words, which you then linked to what you wanted to remember.

Have a look at https://en.wikipedia.org/wiki/Mnemonic_major_system it's not the system I used, but the DOS program I learned from isn't online anymore.

This works really well.

I remember winning a bet about who could retain a 30 (or 20 ?) digit number the longest - I won.

I also used this in primary school to memorize schoolwork for exams, etc.

Despite not using it actively for years I can remember the phonetic alphabet and can still "transcode" numbers to words to images and back well enough. I suspect I might be using a snatch of it here and there for a bit of a memory boost once every few months or so.

I'm the end I abandoned the technique, because it felt like I was "polluting" my memory with extraneous and distracting information.

Reading about memory palaces now make me think of trying them out again, it sounds like they bypass the noisy/distracting aspects of transcoding the information to nonsense associations to make them stand out.

I've taught the loci system to my son in the original Greek context to memorize speeches and they work well.

This is the number system explained in The Memory Book linked by joverholt above.

https://news.ycombinator.com/item?id=28642747