My son did after school classes in abacus and learned how to use do the maths without the abacus, using his hands or just mentally. Even now almost a decade later her can still do some pretty impressive maths in his head using those skills. Or even more impressive is his ability tally quickly. Just today we were talking about how most animals have a common, short name and a longer scientific one. As an example we used a spider near us, it's scientific name is eriophora transmarina and he commented in about two seconds that it had 8 syllables in its name, the same as its full common name. I don't know about others but I had to count three times before I was sure it was 8.