anchor.diff:            (not (dividesp n 11))) nil)
       (t (definitely-palindrome-p n))))
   
  -(defun sum (sequence)
  +(defun sum (sequence &key key)
     (iterate (for n :in-whatever sequence)
  -           (sum n)))
  +           (sum (if key
  +                  (funcall key n)
  +                  n))))
   
   (defun divisors (n)
     (sort (iterate (for i :from 1 :to (sqrt n))
  
positive.code:   ;; What is the sum of the digits of the number 2^1000?
    (sum (digits (expt 2 1000))))
  
  
  ;;;; Tests --------------------------------------------------------------------
  (def-suite :euler)
  
negative.code: (test p14 (is (= 837799 (problem-14))))
  (test p15 (is (= 137846528820 (problem-15))))
  (test p16 (is (= 1366 (problem-16))))
  (test p17 (is (= 21124 (problem-17))))
  
  
  ;; (run! :euler)
  