anchor.diff:  (test p40 (is (= 210 (problem-40))))
   (test p41 (is (= 7652413 (problem-41))))
   (test p42 (is (= 210 (problem-42))))
  +(test p43 (is (= 16695334890 (problem-43))))
   
   
   ;; (run! :euler)
  
positive.code:   "
    (equal (range start (1+ end))
           (sort (digits integer) #'<)))
  
  
  (defun-inline digits< (n digits)
  
negative.code:   ;; and is also prime.
    ;;
    ;; What is the largest n-digit pandigital prime that exists?
    (iterate
      ;; There's a clever observation which reduces the upper bound from 9 to
      ;; 7 from "gamma" in the forum:
      ;;
      ;; > Note: Nine numbers cannot be done (1+2+3+4+5+6+7+8+9=45 => always dividable by 3)
      ;; > Note: Eight numbers cannot be done (1+2+3+4+5+6+7+8=36 => always dividable by 3)
      (for n :downfrom 7)
      (thereis (apply (nullary #'max)
                      (remove-if-not #'primep (pandigitals 1 n))))))
  
  (defun problem-42 ()
    ;; The nth term of the sequence of triangle numbers is given by, tn = ½n(n+1);
  