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Stored size: 832 Bytes
Contents
(ns nth-prime)
(defn sqrt
"Wrapper around java's sqrt method."
[number]
(int (Math/ceil (Math/sqrt number))))
(defn divides?
"Helper function to decide if a number is evenly divided by divisor."
[number divisor]
(zero? (mod number divisor)))
(defn- prime-by-trial-division?
"Simple trial division prime check."
[number]
(empty? (for [n (range 3 (inc (sqrt number)) 2) :when (divides? number n)] n)))
(defn prime? [number]
(or (= 2 number)
(and (odd? number) (prime-by-trial-division? number))))
(defn next-prime [start]
(loop [n (inc start)]
(if (prime? n)
n
(recur (inc n)))))
(def primes (iterate next-prime 1))
(defn nth-prime [index]
(when-not (pos? index)
(throw (IllegalArgumentException. "nth-prime expects a positive integer for an argument")))
(nth primes index))
Version data entries
289 entries across 289 versions & 1 rubygems