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

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

He is immersed in the study of panmagic squares.

He is a perfectionist, and his approach to work is very strict.

He is an expert in ethology, and his research is highly regarded worldwide.

He likes to take a walk in the park at dusk.

He is the type of person who thinks it's a moonlit night if it's bright, so he only has a one-sided perspective.

He thought deeply and said, 'I think, therefore I am.'

He played a perfect fifth scale on the piano.

He is a perfectionist, so he is very strict about his work.