# Deficient number

From Number

This article defines a property that can be evaluated for a natural number, i.e., every natural number either satisfies the property or does not satisfy the property.

View a complete list of properties of natural numbers

## Contents

## Definition

A natural number is termed a **deficient number** if , where denotes the divisor sum function. In other words, is greater than the sum of all its proper positive divisors.

## Relation with other properties

### Opposite properties

- Perfect number: This requires .
- Abundant number: This requires .

### Stronger properties

- Almost perfect number: A natural number such that .