## `numlib::sumdivisors` -- sum of divisors of an integer

#### Introduction

`numlib::sumdivisors``(n)` returns the sum of the positive divisors of the integer `n`.

#### Call(s)

`numlib::sumdivisors(n)`

#### Parameters

`n` | - | an integer

#### Returns

`numlib::sumdivisors``(n)` returns a nonnegative integer.

#### Related Functions

`numlib::sigma`, `numlib::divisors`, `numlib::numdivisors`

#### Details

- `numlib::sumdivisors``(0)` returns `0`.
- `numlib::sumdivisors` returns the function call with evaluated argument if the argument is not a number.
- `numlib::sumdivisors` returns an error if the argument evaluates to a number of wrong type.
- `numlib::sumdivisors``(n)` is the same as `numlib::sigma``(n,1)`.

#### Example 1

The sum of the positive divisors of 120 is 360:

    >> numlib::sumdivisors(120)

                                        360

#### Example 2

The sum of the positive divisors of -63 is 104:

    >> numlib::sumdivisors(-63)

                                        104

#### Background

- Internally, `ifactor` is used for factoring `n`.

#### Changes

- no changes

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