# numlib::sumOfDigits

Sum of digits of an integer

### Use only in the MuPAD Notebook Interface.

This functionality does not run in MATLAB.

## Syntax

```numlib::sumOfDigits(`n`, <`base`>)
```

## Description

`numlib::sumOfDigits(n, base)` computes the sum of digits of `n` in the given base `base`); if the base is not given, it defaults to 10.

The sum of digits may be larger than the base. For certain purposes (testing divisibility by b - 1, where b is the base), it may be useful to apply `numlib::sumOfDigits` over and over to the result. This is not done automatically. See Example 2.

## Examples

### Example 1

We compute the decimal and the binary sum of digits of 11:

`numlib::sumOfDigits(11), numlib::sumOfDigits(11, 2)`

### Example 2

We want to test whether 9 divides a given number, using the school method:

```n:= 24373463462374324: repeat n:= numlib::sumOfDigits(n); print(n) until n < 10 end: delete n:```

This only makes sense for demonstration purposes, as the following command achieves the same but much faster:

`24373463462374324 mod 9`

## Parameters

 `n` Non-negative integer `base` Integer greater than one

## Return Values

Non-negative integer