What is is 20 and 18 weird?

Here's some information about whether 20 and 18 are considered weird numbers:

A weird number is a natural number that is abundant (the sum of its proper divisors is greater than the number itself) but is not a semiperfect number (it cannot be expressed as the sum of some of its proper divisors).

• 18: The proper divisors of 18 are 1, 2, 3, 6, and 9. Their sum is 1 + 2 + 3 + 6 + 9 = 21. Since 21 > 18, 18 is an abundant number. However, 18 = 9+6+3 or 18= 9+6+2+1, so it is a semiperfect number. Therefore, 18 is not a weird number.

• 20: The proper divisors of 20 are 1, 2, 4, 5, and 10. Their sum is 1 + 2 + 4 + 5 + 10 = 22. Since 22 > 20, 20 is an abundant number. However, 20 = 10 + 5 + 4 + 1, so it is a semiperfect number. Therefore, 20 is not a weird number.

The smallest weird number is 70.