(4) A number in which the sum of all its proper factors is less than the number. Example: 10 is a deficient number because the sum of its proper factors is 1 + 2 + 5 = 8 and 8 is less than 10.

A number whose proper factors sum up to less than the number itself. For example, the proper factors of 10 are 1, 2, and 5, which sum to 8.

A positive integer that is larger than the sum of its proper divisors.

a composite number in which the sum of its factors is less than the given number

A deficient number is number (an integer) for which the sum of its proper factors (divisors) is less than the number itself. For example, 9 is a deficient number because the proper divisors of 6 are 1 and 3 which add up to 4, which is less than 9. Compare with abundant number, perfect number.

In mathematics, a deficient number or defective number is a number n for which Ïƒ(n) < 2n. Here Ïƒ(n) is the divisor function: the sum of all positive divisors of n, including n itself. An equivalent definition is that the sum of all proper divisors of the number (divisors other than the number itself) is less than the number.