I memorized a bunch of these for high school math competitions.  You got very familiar with squares up to 100, prime numbers up to 100, converting fractions and repeating decimals.  A sample test from back in the day: <a href="http:&#x2F;&#x2F;www.texasmath.org&#x2F;DL&#x2F;NS&#x2F;NS9394.pdf" rel="nofollow">http:&#x2F;&#x2F;www.texasmath.org&#x2F;DL&#x2F;NS&#x2F;NS9394.pdf</a>
Of course, I&#x27;ve forgotten most of the tricks because they were so specific to the test.