After the fourth round, five more 4clojure.com solutions:

;;; Problem 45 - Intro to Iterate
(deftest test-problem-45
  (let [v1 [1 4 7 10 13] 
        __ v1]
    (is (= __ (take 5 (iterate #(+ 3 %) 1))))))
 
;;; Problem 44 - Rotate Sequence
(deftest test-problem-44
  (let [v1 (fn [n xs] (let [k (mod n (count xs))] (concat (drop k xs) (take k xs))))
        __ v1]
    (is (= (__ 2 [1 2 3 4 5]) '(3 4 5 1 2)))
    (is (= (__ -2 [1 2 3 4 5]) '(4 5 1 2 3)))
    (is (= (__ 6 [1 2 3 4 5]) '(2 3 4 5 1)))
    (is (= (__ 1 '(:a :b :c)) '(:b :c :a)))
    (is (= (__ -4 '(:a :b :c)) '(:c :a :b)))))
 
;;; Problem 43 - Reverse Interleave
(deftest test-problem-43
  (let [v1 (fn [xs n] (partition (/ (count xs) n) (apply interleave (partition n xs)))) 
        __ v1]
    (is (= (__ [1 2 3 4 5 6] 2) '((1 3 5) (2 4 6))))
    (is (= (__ (range 9) 3) '((0 3 6) (1 4 7) (2 5 8))))
    (is (= (__ (range 10) 5) '((0 5) (1 6) (2 7) (3 8) (4 9))))))
 
;;; Problem 42 - Factorial Fun 
(deftest test-problem-42
  (let [v1 #(apply * (range 1 (inc %)))
        __ v1]
    (is (= (__ 1) 1))
    (is (= (__ 3) 6))
    (is (= (__ 5) 120))
    (is (= (__ 8) 40320))))
 
;;; Problem 41 - Drop Every Nth Item
(deftest test-problem-41
  (let [v1 (fn [xs n] (apply concat (map #(take (dec n) %) (partition-all n xs))))
        __ v1] 
    (is (= (__ [1 2 3 4 5 6 7 8] 3) [1 2 4 5 7 8]))
    (is (= (__ [:a :b :c :d :e :f] 2) [:a :c :e]))
    (is (= (__ [1 2 3 4 5 6] 4) [1 2 3 5 6]))))
 
(run-tests)