Question

145 is a curious number, as $1! + 4! + 5! = 1 + 24 + 120 = 145$.

Find the sum of all numbers which are equal to the sum of the factorial of their digits.

Note: as $1! = 1$ and $2! = 2$ are not sums they are not included.

Clojure

#!/usr/bin/env clojure
(defn factorial [n]
  (if (or (= n 1) (= n 0)) 
    1 
    (* n (factorial (- n 1)))))

(defn digits [number]
  (map #(- (int %) 48) (str number))) 

(defn curious? [number]
  (and (= (apply + (map factorial (digits number))) number)
       (> (count (digits number)) 1)))

(println (reduce + (filter curious? (range 50000))))

$ time clojure curious.clj
real   0m1.027s
user   0m2.166s
sys    0m0.076s

Haskell

factorial :: Int -> Int
factorial n = product [1..n]

digits :: Int -> [Int]
digits 0 = []
digits n = r : digits q
    where (q, r) = quotRem n 10

curious :: Int -> Bool
curious n = n == sum (map factorial (digits n))

main :: IO ()
main = print $ sum $ filter curious [10..50000]

$ ghc -O2 -o curious curious.hs
$ time ./curious
real   0m0.010s
user   0m0.010s
sys    0m0.000s

Ruby

#!/usr/bin/env ruby
puts (0..50000).select { |i|
  i.to_s.length > 1 && i == i.to_s.each_char.map { |d| (1..d.to_i).reduce(1, :*) }.reduce(:+)
}.reduce(:+)

$ time ruby curious.rb
real   0m0.256s
user   0m0.241s
sys    0m0.016s

Scheme

(define (factorial n)
  (apply * (iota n 1)))

(define (digits n)
  (if (zero? n)
    '()
    (cons (remainder n 10) (digits (quotient n 10)))))

(define (curious? n)
  (and (= (apply + (map factorial (digits n))) n)
       (> (length (digits n)) 1)))

(display (apply + (filter curious? (iota 50000))))
(newline)

$ time mit-scheme --quiet < curious.scm
real   0m0.387s
user   0m0.331s
sys    0m0.055s