I am doing the Project Euler challenge in Clojure and I want to find the sum of all the even numbers in a fibonacci sequence up to a certain number. The code for a function that does this is below. I know there are quicker and easier ways of doing this, I am just experimenting with recursion using loop and recur. However the code doesn't seem to work it never returns an answer. (defn fib-even-sum [upto] (loop [previous 1 nxt 1 sum 0] (if (or (<= upto 1) (>= nxt upto)) sum) (if (= (mod nxt 2) 0) (recur nxt (+ previous nxt) (+ sum nxt)) (recur nxt (+ previous nxt) sum)))) I was not sure if I could do recur twice in the same loop or not. I'm not sure if this is causing the problem?