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

He solved a large number of problems.

Understanding numbers is important for solving math problems.

He was bedridden with illness for several days.

I can't solve this problem because there are too many numbers.

He has confidence in his own abilities.

The Reynolds number is an important concept in fluid dynamics.

Kazuto-kun is my best friend.

Kazuo is my best friend.

Masakazu is my best friend.