Your short-term memory has a limited capacity. It can hold information for up to 30-40 seconds. Young people, up to approx. 14 years old, can remember and process 3-7 different subjects at the same time. From the age of 14 onward, this increases to 5-9 simultaneous subjects in short-term memory. So… what can you do to remember more and better?

piYou can create and use chunks, meaning blocks, so a chunk means a block of information that you remember and work with, as if it were a single element.
Chunking occurs naturally. For example: the word “pythagoras” probably makes you think of Pythagoras’ theorem (a2 + b2 = c2), including all you know about it – if you spend some time on it, you will realize you actually know a lot more about it than you might realize.
Chunking assumes that you consciously group topics together and find a common denominator for it, so that you can remember and work with it as a single concept. The advantage of discovering such a common denominator yourself, is that you own that concept yourself, and you will remember it much better.

Make a structure of what you want to learn – you can e.g. use a mind map, 2-column note, or a top-down chart where you specify downward, and generalize upward.

If you want to remember the first ten decimal numbers of π, instead of thinking one-four-one-five-nine-two-six-five-three-five (which is 10 units) you can think fourteen, fifteen, ninetytwo, sixtyfive, thirty-five (which is 5 units).

By the way:
Marisca Milikowski and Jan Elshout wrote an interesting dissertation on remembering numbers between 0 and 100. There is supposedly a difference between single-digit numbers, the numbers 10-19, double numbers (33, 44, 55, etc.), numbers from the multiplication tables (49, 56 , 73, etc.) and the other numbers. The latter group is the most difficult to remember and use. You can find the dissertation here: /…/What_makes_a_number_easy.pdf