1.21

Exercise 1.21: Use the smallest-divisor procedure to find the smallest divisor of each of the following numbers: 199, 1999, 19999.

(define (smallest-divisor n) 
    (find-divisor n 2))

(define (square x) (* x x))

(define (remainder a b) (cond ((< (- a b) b) (- a b))
    (else (remainder (- a b) b))
))

(define (find-divisor n test-divisor)
    (cond ((> (square test-divisor) n)
        n)
        ((divides? test-divisor n)
            test-divisor)
        (else (find-divisor
                n
                (+ test-divisor 1)))))

(define (divides? a b)
    (= (remainder b a) 0))

(smallest-divisor 199)

(smallest-divisor 1999)

(smallest-divisor 19999)