1 665c255d 2023-08-04 jrmu (defun filtered-accumulator (combiner null-value term a next b filter)
 2 665c255d 2023-08-04 jrmu   (cond ((> a b) null-value)
 3 665c255d 2023-08-04 jrmu 	((funcall filter a)
 4 665c255d 2023-08-04 jrmu 	 (funcall combiner
 5 665c255d 2023-08-04 jrmu 		  (funcall term a)
 6 665c255d 2023-08-04 jrmu 		  (filtered-accumulator combiner null-value term (funcall next a) next b filter)))
 7 665c255d 2023-08-04 jrmu 	(t (filtered-accumulator combiner null-value term (funcall next a) next b filter))))
 8 665c255d 2023-08-04 jrmu (defun sum-squares-of-primes (a b)
 9 665c255d 2023-08-04 jrmu   (filtered-accumulator #'+ 0 #'square a #'1+ b #'prime?))
10 665c255d 2023-08-04 jrmu (defun product-of-relatively-prime (n)
11 665c255d 2023-08-04 jrmu   (defun relatively-prime-to-n? (k)
12 665c255d 2023-08-04 jrmu     (= (gcd k n) 1))
13 665c255d 2023-08-04 jrmu   (filtered-accumulator #'* 1 #'identity 1 #'1+ (1- n) #'relatively-prime-to-n?))