### On near-perfect numbers

Min Tang, Xiaoyan Ma, Min Feng (2016)

Colloquium Mathematicae

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For a positive integer n, let σ(n) denote the sum of the positive divisors of n. We call n a near-perfect number if σ(n) = 2n + d where d is a proper divisor of n. We show that the only odd near-perfect number with four distinct prime divisors is 3⁴·7²·11²·19².