When I was four or five years old, my parents used to show off my amazing memory. They'd have me stand in the middle of a room, in front of their guests, and say, "Mary, divide 8,920,264,894,029,253 by 3,982,420." In a minute or so, I would give the correct answer. I could do the same with multiplication, addition or subtraction.
I can't do it any more. Somewhere around high school, it faded away. But well into adulthood I was able to remember any number I heard. My head was full of telephone numbers, social security numbers, and dates. I could figure out how much a job would cost a client and how much they had paid last month and how much they owed without consulting my records. I didn't need tricks to remember, I just did... but I often connected the numbers, for example, 615-1215 was a phone number but it was also the date King John signed the Magna Carta. It rang a bell in my head just like 911-2001 would ring a bell in yours.
I can't do that any more, either. I have a cell phone. If I lost it I would not be able to call anyone in my family. I see the numbers every day, but I don't remember them. Ask me how much 6 times 7 is, and it takes effort to remember. I stand there looking at a measuring cup... um... 1/2 cup of water plus 1/3 cup of oil would come out... where?
I think I birthed it out of me. My children can do these tricks now - and have every bit as much appreciation for the skill as I did. lol