Clojure has clojure.math.combinatorics which contains many convenient functions. So arguably the "idiomatic" way to do what you did in Clojure would be to import/require clojure.math.combinatorics and then simply call combinations with n = 2.
...> (comb/combinations [1 2 3 4] 2)
((1 2) (1 3) (1 4) (2 3) (2 4) (3 4))
For this to work you'll need to first add the correct dependency.
As I write this the latest version is: [org.clojure/math.combinatorics "0.0.7"]
I did then require it ":as comb
":
(:require [clojure.math.combinatorics :as comb]
In case you don't want to use math.combinatorics, you can edit your question to precise it and I'll delete my answer.