Generally, fewer is used when a number of things can be counted (“fewer problems”) and less is used when an amount is measured (“less trouble” or “less time”). However, this is not a strict rule and there are accepted instances of less being used with countable amounts such as “250 words or less,” “3 items or less,” and especially with money (“less than $20”) and distance (“less than 3 miles”). Note that in all these cases, the things considered are often thought of as amounts rather than numbers.

https://www.merriam-webster.com/grammar/fewer-vs-less

“38,000 mentions”, so “less” is appropriate.