Deficient number

A deficient number is an integer which factors (including that number) is less than twice that number.

Example
See also: 32 32 is a deficient number.

The factors of 32 are: 1, 2, 4, 8, 16 and 32, which add up to 63.

As 63 is less than 2 × 32, which is 64 by 1, 32 is a deficient number.

As the deficiency of 32 is 1, 32 is also a almost perfect number.

Types of numbers always deficient numbers

 * Prime numbers. A prime number has deficiency p - 1, where p is the prime number.
 * Powers of 2. As shown in the example above, a power of 2 has deficiency 1. It is also known as an almost perfect number.
 * Powers of prime numbers.