Because all of its factors also known as 13 and 1 add up to be more than the number itself 13.
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13 is deficient.
The factors of 26 are 1, 2, 13. And if you add them together (1+2+13) the answer is 16 which is less than 26 so it is an deficient number.
55 is deficient.
NO- 24 is not deficient.
It's deficient