What is is 19 and 17 weird?

The numbers 19 and 17 are not considered "weird" in a mathematical sense. In number theory, a "weird number" is defined as a natural number that is abundant but not semiperfect. An abundant number is a number for which the sum of its proper divisors (divisors excluding the number itself) is greater than the number. A semiperfect number is a number for which some subset of its proper divisors sums to exactly the number itself.

For example, 70 is a weird number because:

• It is abundant: the sum of its proper divisors (1, 2, 5, 7, 10, 14, 35) is 74, which is greater than 70.
• It is not semiperfect: no subset of those divisors sums to exactly 70.

With this definition of weird numbers in mind, neither 19 nor 17 qualify as weird:

• Both 19 and 17 are prime numbers, meaning their only proper divisor is 1.
• The sum of the proper divisors of 17 and 19 is 1, which is less than both numbers.

Therefore, neither number is abundant, and consequently, neither is weird. In casual contexts, if someone refers to a number as "weird," they might be speaking humorously or personally rather than based on mathematical properties.