Double factorial

Double factorial is a method of calculating how many times a number is repeated in a geometric equation. This way, we can calculate the number of times a product is used in its life-time.

The double factorial of n is written as . When n is a positive odd integer,  is defined as . When n is an positive even integer,  is defined as . By definition, .

 Related pages 

 Factorial
 Permutation

 References 

Category:Integer sequences
Category:Number theory