The phrase "a huge decrease in the number" is correct and usable in written English.
You can use it when discussing a significant reduction in quantity or figures, often in contexts like statistics, research, or reports.
Example: "The recent study showed a huge decrease in the number of participants compared to last year."
Alternatives: "a significant drop in the number" or "a large reduction in the number."
In Britain over the past decade we have seen a huge decrease in the number of nightclubs and one of the main reasons has been a new approach, by police and local authorities, who now seek to hold premises responsible for the behaviour of their customers.
"I think it would lead to a great decrease in the number of lemon law claims that would be filed by consumers, and a huge decrease in the number of class-actions that could be filed by dissatisfied customers against manufacturers for product defects," she said.
Monica happens to live in a country where the business of birthing babies has changed dramatically in recent years: The Ministry of Health has made family-planning education and services so readily available, that Monica herself has seen a huge decrease in the number of births she assists--from nearly 100 in her early years, to about 30 births per month now.
However, in dramatic contrast to the effects of TbKIN13-1 depletion, knockdown of these kinesin-like proteins results in a huge decrease in the number of observed spindles.
There have been huge decreases in the number of students coming from Latin America, Russia and Europe.
Environmentalists and birders are tracking the crab population as well, because a huge surge in the number of crabs collected for bait in the last decade, and a decrease in the number of the shorebirds that feed on them -- red knots in particular -- have caused alarm.
Interestingly, in some subgroups we observed a huge expansion in the number of family members.
A 2013 Royal College of Nursing report showed a 12.7percentt decrease in the number of places for student nurses.
