Kaprekar’s constant is 6174. The Kaprekar Routine arranges four digits
(zeros are appended to the number if it’s less than 4 digits) in
descending and ascending order, subtracts those two numbers, and repeats
the process until the difference is 0 (degenrate case) or 6174
(Kaprekar’s constant). The color is HSL with a scale of 0 to 300 in the
domain of 1 to 7 (minimimum and maxium iterations to reach Kaprekar’s
constant) for hue, 1 for saturation, and .5 for lightness.

I created this because I wanted to visualize Kaprekar’s constant in
some way. This Wolfram MathWorld article on the Kaprekar Routine
has a compelling image that is inspired by the cover of *The Mathematics Teacher*.
From there, I decided to research some visualization techniques by
recreating it with d3.js and adding some extra
features (sorting, highlighting, and showing the routine).

I first heard of Kaprekar’s constant after looking at the Google New
York office.
Apparently, there are about one-half of Kaprekar’s constant Googlers
there.

## References