File:Deficient_number_Cuisenaire_rods_8.png · Wikimedia Commons · See Wikimedia Commons
deficient number
Sign in to savenatural integer number for which the sum of its proper strict divisors (other than itself) is less than the number itself
~4 min read
Encyclopedic overview
Demonstration, with Cuisenaire rods, of the deficiency of the number 8
In number theory, a deficient number or defective number is a positive integer n for which the sum of divisors of n is less than 2n. Equivalently, it is a number for which the sum of proper divisors (or aliquot sum) is less than n. For example, the proper divisors of 8 are 1, 2, and 4, and their sum is less than 8, so 8 is deficient.
Excerpted from Wikipedia’s “deficient number” article, available under the CC BY-SA 4.0 licence.