Back عدد ناقص Arabic Niver diouerus Breton Nombre deficient Catalan Deficientní číslo Czech Defektivt tal Danish Defiziente Zahl German Ελλιπής αριθμός Greek Nùmer difetìv EML Manka nombro Esperanto Número defectivo Spanish
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.
Denoting by σ(n) the sum of divisors, the value 2n – σ(n) is called the number's deficiency. In terms of the aliquot sum s(n), the deficiency is n – s(n).