Sum digits of an integer
From Fōrmulæ wiki
This page is a solution to the task Sum digits of an integer in the Rosetta Code, written in Fōrmulæ.
Description (from Rosetta Code)
Task
Take a Natural Number in a given base and return the sum of its digits:

Program
Use cases
Extras
The following is the plot of the function, to numbers 1 .. 300, in base 10: