A common problem that we can solve with recursion is calculating the factorial. >Quick mathematics refresher about factorials: >The factorial of a number is the product of all positive integers bigger than 0, up to the number itself. So for example, the factorial of seven is 7 * 6 * 5 * 4 * 3 * 2 * 1. You can write this as 7!. How are recursive functions going to help us calculate the factorial? We are going to call the function with a lower number until we reach 0. In this exercise, we will use recursion to calculate the factorial result of a numeric value set as the argument of a function. 1. Create a function that contains a condition within it checking if the argument value is `0`. 2. If the parameter is equal to 0, it should return the value of `1`. Otherwise, it should return the value of the argument multiplied by the value returned from the function itself, subtracting one from the value of the argument that is provided. This will result in running the block of code until the value reaches `0`. 3. Invoke the function, providing an argument of whatever number you want to find the factorial of. The code should run whatever number is passed initially into the function, decreasing all the way to 0 and outputting the results of the calculation to the console. It could also contain a console.log() call to print the current value of the argument in the function as it gets invoked. 4. Change and update the number to see how it affects the results. ```js function calcFactorial(nr) { console.log(nr); if(nr === 0) { return 1; } else { return nr * calcFactorial(--nr); } } console.log(calcFactorial(4)); ``` Represent in your favorite programming language a simple example of a recursive function and we'll see which one is more complex to implement.

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