(define (div a b)
  (zero? (remainder a b)))

(define (next start)
  (let loop ((current (+ (* 2 start) 1)))
    (if (prime? current)
      current
      (loop (+ current 1)))))

(define (prime? x)
  (and (not (div x 2))
       (let loop ((i 3))
         (or (> (* i i) x)
             (and (not (div x i))
                  (loop (+ i 2)))))))

(define (run start)
  (display start) (newline)
  (unless (= 650680571 start)
    (run (next start))))

(run 307)