The adjective phrase “most number” may sound decidedly odd to some ears, but I daresay it’s grammatically correct in the sense of “maximum”—the sense intended for it in within the strict letter-count confines of that headline.
Now, as you suggested, let’s try substituting “highest” or “greatest” for “most number” in that headline and see what happens:
“Scientist says 150 is the highest number of friends one can comfortably have”“Scientist says 150 is the greatest number of friends one can comfortably have”My ear finds each of these two headlines odder than odd, and I think yours will, too.
As to your other question: Can we drop “most” from that headline?
Let’s also try doing that:
“Scientist says 150 is the number of friends one can comfortably have”I must say it looks like a three-legged chair with one of the legs lopped off—and it’s also seriously flawed semantically. Without “most,” that sentence wrongly and absurdly implies that one can’t comfortably have any number of friends below 150.
The fact is that despite intermittent attacks on its grammatical legitimacy by both English-savvy and less-than-English-savvy people, “most number” is perfectly acceptable English.
For, really now, can we actually consider the following sentences using “most number” grammatically faulty?
“What is the
most number of languages spoken by a single person?”
“Does English have the
most number of irregular verbs among the world’s top 10 widest spoken languages?”
Whatever the answer to those two questions, I think their use of “most number” is beyond reproach grammatically, semantically, and idiomatically. But you don’t have to take my word for it, Alek. Take a look at this passage from an actual media release of
the American Society of Magazine Editors announcing the nominations to its 2009 best magazine journalism awards:
“GQ was nominated for eight awards, including two nominations for Reporting. Eight is the
most number of nominations GQ has ever received in any single year.” (italicizations mine)
With that, I rest my case for “most number.”