Have different kids from each class pick a number 1-9. Each class should have 4 different digits. Make a poster of each for your wall. Have a running contest between classes.
Ask students to use those digits to find all of the numbers from 1-100. They can use +, -, *, /, and (). They can use one of their digits as an exponent. You might want to include the digit 2 in each class for this purpose. I allowed them to use the square root as well, even though technically it is a rational exponent.
Once they’re stumped, suggest (if someone doesn’t ask) that they “squeeze” number together – i.e., squeeze 1 and 9 to make 19 to get larger numbers.
Introduce the factorial eventually. 4! = 4*3*2*1
Have students work on it and when they get one, they must have 2 other students verify it before they bring it to you to add to the poster. Let them write it on the poster and initial it!
If there seems to be one particularly difficult number to find, make a wanted poster. Post it near the class poster. Offer a reward of a power-aid or whatever.