There are 104 options when choosing elements out of available elements and repetitions are permitted.
When choosing elements out of available elements and repititions are not permitted there are options. This is called the number of permutations of out of elements.
When repetition is not permitted, you get a multiplication of a series of decreasing successive numbers. The multiplication of the decreasing series of numbers through is called 10 factorial.
You write this as 10!, so .
It has been agreed that . The calculator has a function that calculates factorials.
When dealing with permutations you also encounter a decreasing series of numbers.
This series, however, does not always end with the number 1.
Your calculator has a special function to calculate permutations like .