MathDB

Let

d(n)

denote the number of positive divisors of

n

. For positive integer

n

we define

f(n)

f(n) = d\left(k_1\right) + d\left(k_2\right)+ \cdots + d\left(k_m\right),

where

1 = k_1 < k_2 < \cdots < k_m = n

are all divisors of the number

n

. We call an integer

n > 1

almost perfect if

f(n) = n

. Find all almost perfect numbers.
Paulius Ašvydis

Problem Statement