Here's an example: "We've seen the Yankees play many, many times."
The word "many", in both cases, is an adjective that describes "times", which is used here as a noun. When two or more adjectives get together in a sentence, a comma's supposed to show up and keep them apart. It makes for an orderly, smooth flow of words. The double appearance of "many" isn't a valid excuse for the comma's absence. BTW, no commatization needed between "many" and "times."
Hope this helps!