Or, an alphabetical listing of general categories ~
Moebius (Mobius) Strip: Discover how to make a Moebius strip, as well as some very cool things about it.
Multiply by 5 the easy way
Multiply by 9 the easy way: multiply single digits by 9, and larger numbers when all the digits are the same, like 88888 x 9
Scratch Addition: Quick and easy way to add a column of single digit numbers using the Scratch or Dot Method.
Squaring numbers whose digits are all ones: like 11 x 11 or 11111 x 11111, etc.
Square Numbers that end in 5 such as 85 time 85, etc.