I don't really bother to keep them memorized 'uncompressed', I remember a jumble of them that stuck for one reason or another (eg 7x7=49 just sort of makes me feel 'satisfied' somehow) and just have built up an instinct to 'disassemble' the multiplication into the ones I remember more strongly. Eg for 7x8, while I did instantly think 56, I still automatically checked it as 7x7+7. This also helps with larger multiplications, since my first instinct is to simplify the problem to something that is trivially solvable and checkable.
Nowadays I don't often have to use these tricks, the vast majority of the time I'm already typing into something that can give me the result (a browser, or a terminal), or am in no rush and can just use my phone or watch. At most it makes for an occasionally nice trick to show in conversations.
Nowadays I don't often have to use these tricks, the vast majority of the time I'm already typing into something that can give me the result (a browser, or a terminal), or am in no rush and can just use my phone or watch. At most it makes for an occasionally nice trick to show in conversations.