Some useful math functions for lisp.

math-misc.lsp

(defun cube-root (n)
  ;; Calculates the Cube Root of n.
  (expt n 1/3))


(defun factors (n &aux (lows '()) (highs '()))
  ;; We iterate in the range 1..sqrt(n) collecting ‘low’ factors and corresponding ‘high’ factors, 
  ;; and combine at the end to produce an ordered list of factors.
  ;; http://rosettacode.org/wiki/Factors_of_an_integer#Common_Lisp
  (do ((limit (isqrt n)) (factor 1 (1+ factor)))
      ((= factor limit)
       (when (= n (* limit limit))
         (push limit highs))
       (nreconc lows highs))
    (multiple-value-bind (quotient remainder) (floor n factor)
      (when (zerop remainder)
        (push factor lows)
        (push quotient highs)))))

(defun primep (n)
  ;; Tests if the numbers is a Prime.
  (= 2 (length (factors n))))

(defun slope (first-point last-point)
  ;; Calculates the slope between 2 Points
  (let ((change_x (float (- (pop last-point) (pop first-point)))) 
        (change_y (float (- (pop last-point) (pop first-point)))))
    (float (/ change_y change_x))))