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.

They appear to be antagonistic on the surface, but in reality, they are seemingly not part of the same group.

A row vector is one of the basic concepts in linear algebra.

This book was issued last year.

I went to the office to issue a new passport.

He achieved a quick kill in that game.