3
$\begingroup$

A perfect number is a number that is the sum of its proper divisors: $28 = 1 + 2 + 4 + 7 + 14$

Is there a name for numbers whose only proper divisors are $1$, $2$, and $N/2$? For example

$6$ is divisible by $1$, $2$, and $3$

$8$ is divisible by $1$, $2$, and $4$

$34$ is divisible by $1$, $2$, and $17$

Is there a name for these numbers?

  • 1
    Something "unpleasant" that the comment of Aryabhata has received seven votes as "useful".2018-07-29

1 Answers 1

7

Aside from 8 and arguably 2, these are the even semiprimes, Sloane's A100484.