"noticeable number" is correct and usable in written English.
It could be used when referring to a large or obvious quantity, such as "there was a noticeable number of people who had attended the event".
A noticeable number of listeners followed the performance with scores in hand.
Riding on the back of "Boy With a Pipe" are a noticeable number of Picassos from nearly every period.
The orchestra sounds terrific, but Carnegie Hall, usually packed for Chicago Symphony concerts, had a noticeable number of empty seats.
Designed to operate with natural gas, the MGT are devices technologically recent with a noticeable number of functional advantages.
Others might have the inclination of a noticeable number of people at a recent performance by skulking somewhat guiltily out of the theater at intermission.
There are also a noticeable number of women on bicycles and in trousers – two things that Kim Jong-il frowned upon.
On Tuesday, the rapport between the musicians (including noticeable numbers of younger players) and their kinetic conductor was palpable.
The report notes that homosexual men began entering the seminaries "in noticeable numbers" from the late 1970s through the 1980s.
A generation back, when the first single mothers by choice started having kids in noticeable numbers, that sort of barb had real bite.
Among the concertgoers at Avery Fisher Hall on Sunday afternoon were noticeable numbers of people clad in green to profess their cultural solidarity with the National Symphony Orchestra of Ireland in its New York debut.
Mr. Bush and his war cabinet would be wise to see the demonstrators as a clear sign that noticeable numbers of Americans no longer feel obliged to salute the administration's plans because of the shock of Sept. 11 and that many harbor serious doubts about his march toward war.
