almost perfect number
A description sometimes applied to the powers of 2 because the aliquot parts (proper divisors) of 2n sum to 2n - 1. So a power of 2 is a deficient number (one that is less than the sum of its proper divisors), but only just. It isn't known whether there is an odd number n whose divisors (excluding itself) sum to n - 1.
Related category• TYPES OF NUMBERS
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