Mathematical Formulas for Programmer

Below are some of the formulas that can be useful while doing competitive programming.

• 1∗1!+2∗2!+...+x∗x! = (x+1)!−1
• (A+B)%C = (A%C + B%C )%C. 
• (A* B)%C = ((A%C) * (B%C))%C 
• LCM(a, b) = (a * b) / GCD(a, b)
   

I will be adding more formulas to it.
Please comment if you find anything incorrect.