What is a deficient number and how does it relate to a prime number?

Answer by  mathted (27)

A prime number is any number greater than 1 that has no factors other than the number 1 and itself. A deficient number is a positive integer that is larger than the sum of all of its factors (not including the number itself). Any prime number must be a deficient number, because 1 is always less than the prime itself.

Answer by  MathTeacher (299)

A deficient number is a number n for which the sum of all positive divisors of n, including n itself is less than 2n. All odd numbers with 1 or 2 distinct prime factors are deficient.