Is it possible for a computer to generate a totally random number? if so, how?

I cannot comprehend how is it possible for a computer to generate a totally random number. Also I can't stress enough when I write "TOTALLY Random".

Suppose, as an example, A programmer might just write such algorithm. Though extremely less probable, It is always possible to do some kind of reverse engineering in the code that had made the illusion of that number being totally "random" to be perceived by human brain. How is it possible to write such algorithm where the generated number is not through a set of logic that can be penetrated.

I do not expect any code necessarily, Just a brief explanation will do. Thanks