(define repeatedly-double ; doubles b (lambda (b n) ; n times, n >= 0 (if (= n 0) b ; not squared at all (repeatedly-double (+ b b) (- n 1)))) > (repeatedly-double 4933 10) 5051392So there are approximately 5,051,392 digits in the 24th Fermat number, the first Fermat number whose primality is unknown.