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Proper divisors: Difference between revisions
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the number(s) with the most divisors between 1 and 20000 is/are:
[15120, 18480] with 79 divisors</pre>
=={{header|Common Lisp}}==
<lang lisp>(defun proper-divisors-recursive (product &optional (results '(1)))
"(int,list)->list::Function to find all proper divisors of a +ve integer."
(defun smallest-divisor (x)
"int->int::Find the smallest divisor of an integer > 1."
(if (evenp x) 2
(do ((sd 3 (+ sd 2)))
((or (integerp (/ x sd)) (= sd x)) sd))))
(defun pd-rec (fac)
"(int,int)->nil::Recursive function to find proper divisors of a +ve integer"
(when (not (member fac results))
(push fac results)
(let ((hifac (/ fac (smallest-divisor fac))))
(pd-rec hifac)
(pd-rec (/ product hifac)))))
(pd-rec product)
(butlast (sort (copy-list results) #'<)))
(defun task (method &optional (n 1) (most-pds '(0)))
(dotimes (i 19999)
(let ((npds (length (funcall method (incf n))))
(hiest (car most-pds)))
(when (>= npds hiest)
(if (> npds hiest)
(setf most-pds (list npds (list n)))
(setf most-pds (list npds (cons n (second most-pds))))))))
most-pds)
(defun main ()
(format t "Task 1:Proper Divisors of [1,10]:~%")
(dotimes (i 10) (format t "~A:~A~%" (1+ i) (proper-divisors-recursive (1+ i))))
(format t "Task 2:Count & list of numbers <=20,000 with the most Proper Divisors:~%~A~%"
(task #'proper-divisors-recursive)))</lang>
{{out}}
<pre>CL-USER(10): (main)
Task 1:Proper Divisors of [1,10]:
1:NIL
2:(1)
3:(1)
4:(1 2)
5:(1)
6:(1 2 3)
7:(1)
8:(1 2 4)
9:(1 3)
10:(1 2 5)
Task 2:Count & list of numbers <=20,000 with the most Proper Divisors:
(79 (18480 15120))
NIL</pre>
=={{header|D}}==
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