While listicles with 10 items are the most prevalent (BuzzFeed sells lists of that length to advertisers, Lotan writes), and there are plenty of even-numbered lists, odd numbers have “higher audience score on average” and “the number 29 tends to have an advantage over the rest,” Lotan writes.
If you are chasing clicks, you should definitely read this bit from Poynter. Sometimes science feels so icky.