diff --git a/subjects/collatzcountdown/README.md b/subjects/collatzcountdown/README.md
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--- a/subjects/collatzcountdown/README.md
+++ b/subjects/collatzcountdown/README.md
@@ -2,7 +2,7 @@
 
 ### Instructions
 
-Write a function, `CollatzCountdown`, that returns the number of steps necessary to reach 1 using the collatz countdown.
+Write a function, `CollatzCountdown`, that returns the number of steps necessary to reach 1 using the [collatz countdown](https://en.wikipedia.org/wiki/Collatz_conjecture).
 
 - It must return `-1` if `start` is equal to `0` or negative.