Examples

• Consider the number 81. The sum of its proper divisors is 40, because: 1 + 3 + 9 + 27 = 40. Because 40 < 81, this means that 81 is a deficient number.
• Consider the whole number 20. The sum of its proper divisors is 22, because: 1 + 2 + 4 + 5 + 10 = 22. Because 22 > 20, this means that 20 is not a deficient number.