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

He is immersed in the study of panmagic squares.

This fish is completely farmed, and no capture is done in the natural environment.

His tone of speech is very unique.

You can see the form of 'Renshō' in this ancient document.

His voice is very attractive.

He was showered with jeers.

He underwent vocal cord surgery.

He practices vocalization every day.

He practices every day to pronounce accurately.