LispLabs/lab6.lsp at master · MelnykAndriy/LispLabs · GitHub

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(defun prime-factors-mult (n)
    (labels ((%prime-p (number)
                (when (> number 1)
                    (loop for fac from 2 to (isqrt number) never (zerop (mod number fac)))))

            (%next-prime (number)
                (loop for n from number when (%prime-p n) return n)))

        (macrolet ((%do-primes ((var start end) &body body)
                        `(do ((,var (%next-prime ,start) (%next-prime (1+ ,var))))
                            ((> ,var ,end))
                            ,@body)))
            (let ((primes nil))
                (%do-primes (p 0 n) (push p primes))
                (mapcar (lambda (p)
                            (list p (do ((ntimes-p p (* ntimes-p p))
                                         (ntimes 0 (1+ ntimes)))
                                            ((> (mod n ntimes-p) 0) ntimes))))
                        (reverse (remove-if-not (lambda (p) (zerop (mod n p))) primes)))))))