In mathematics, a perfect number refers to a number where the sum of its divisors, excluding the number itself, equals the number.

In math class, I learned about deficient numbers.

Amicable numbers refer to a pair of natural numbers that have a special relationship in number theory, a branch of mathematics.

What is the play count of this video?

In Japan, 4 and 9 are considered unlucky numbers.

The leading edge of this airplane is very sharp.

Mr. Maenomae is my best friend.

Maoka-san is my best friend.

Mr. Maesato is my best friend.

This rain is a harbinger of the typhoon.