Not much to say about this problem. Everyone’s solution seemed similar to my own, with some minor stylistic variation.

```
(def natural-numbers (iterate inc 1))
(defn square-of-sum [coll]
(expt (reduce + coll) 2))
(defn sum-of-squares [coll]
(reduce + (map #(expt % 2) coll)))
(defn diff-between-squares [coll]
(- (square-of-sum coll) (sum-of-squares coll)))
(diff-between-squares (take 100 natural-numbers))
```

Yes, the definition of natural-numbers is perhaps a bit pedantic, but thought it might be fun to try to ensure I didn’t accidentally take a list of numbers starting at 0 and ending at 99…although technically this might be considered a set of natural numbers as well, according to wikipedia.