Sieve of Eratosthenes in clojure

sieve-of-eratosthenes.clj

(defn multiple?
  "Check if the number-to-check is a multiple of number."
  [number-to-check number]
      (= 0 (mod number-to-check number)))

(defn sieve-of-eratosthenes
  "For the number ranging from 2 to the given number 'upto'(inclusive),
  filters out all the numbers that are not prime and 
  return the prime numbers."
  [upto]

  ; Remove if 1 is present in the first
  (def all-but-one (range 2 (inc upto)))
  
  (def limit (Math/sqrt upto))

  (loop [curr 2 processed [] remaining all-but-one]

    (if (> curr limit)
      (concat processed remaining)
      (recur (second remaining) ; Move the next number
             (conj processed curr) ; Add the current to the processed
             (filter #(not (multiple? % curr)) remaining))))) ; Filter out everything that are multiples


; Verification
; user=> (sieve-of-eratosthenes (range 1 20))
; (2 3 5 7 11 13 17 19)