Using qualtrics feature you can use timing question with descriptive question to show them numbers one after the another and at the end you can ask them to enter the number. Use branch logic to check whether the number was correct or incorrect. Else you can use JS to customize (or build) your own memory task as you want.

Thanks!
How do I show them number after number?

Have a block with timer question and descriptive question one after the another, add page breaks after each descriptive question. Put auto advance after 2 sec for all timer question. You can also do this using loop and merge.