Because Japanese word for "four" sounds exactly like the word for "death" and they consider "nine" to be unlucky, as it sounds like the word for "suffering," there are no rooms numbered 4 or 9 in many hospitals and hotels in Japan.
Western culture's fear of number 13 is evident enough to acquire a name triskaidekaphobia, while tetraphobia is the aversion or fear of number 4, and enneaphobia, the fear of number 9.
