(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)
5051392
So there are approximately 5,051,392 digits in the 24th Fermat number, the
first Fermat number whose primality is unknown.