; solution for http://www.spoj.pl/problems/FCTRL/ (use numbers) (define (fact-iter init n)  (if (= n 1)      init      (fact-iter (* init n) (- n 1)))) (define (fact n) (fact-iter 1 n)) (define (z-iter count x)  (if (<= x 0)      count      (if (not (= (+ (modulo x 10) 1) 1))          count          (z-iter (+ count 1) (/ x 10))))) (define (z n)  (z-iter 0 (fact n))) (define (test)  (map z '(3 60 100 1024 23456 8735373))) (test)