100
This is the rule for the following pattern:
1,1,2,6,24,120
Add 0, then add 1, then add 2, and so on...
Multiply by 1, then multiply by 2, then multiply by 3...
Multiply by 1, then add 1
Multiply by 2, then subtract 1
What is multiply by 1, then multiply by 2, then multiply by 3, and so on