The phrase "a number of formidable" is correct and usable in written English.
It can be used to describe multiple impressive or powerful entities, people, or things in a context where you want to emphasize their strength or capability.
Example: "The team faced a number of formidable opponents during the tournament, each with unique skills and strategies."
Alternatives: "several impressive" or "many powerful".
Even before it can be discussed a number of formidable obstacles would have to be removed, including the signing of a formal peace treaty.
The company will face a number of formidable competitors, including Battlefield-maker Electroficourse and of course, Gameloft and Activision.
A number of formidable figures from the old Negro leagues also deserve plaques in Cooperstown, as do scores of players from the pre-World War II era and a few from the pre-1920 age of the dead ball.
While Pakistan undoubtedly faces a number of formidable challenges between now and May, there is reason for cautious optimism and even hope for Pakistan's struggling democracy.
In conclusion, HIV-associated TBM is a devastating disease and a number of formidable challenges remain.
There are a number of formidable barriers that interferes with chemotherapy treatments in patients with CNS IVL.
She observed that 'there were a number of "pretty formidable" ethical concerns in allowing future trials to go ahead' (Skatsson 2002, 1).
While proud of its accomplishments, the field has embraced bold goals such as ending preventable child and maternal deaths in a generation among a number of other formidable challenges.
The investigation of the health impact of air pollution from point sources in resource poor settings poses a number of difficulties, the most formidable of which is measurement of exposure.
A new wave of interest in West has resulted in a number of books concerned with her formidable feminism, her games with what she would never have wished to call "gender," and her enduring status in the American pop pantheon.
The parasite has a number of tricks, however, that make it a formidable foe.
