(defun myfun (x n) (sqrt (- (expt (+ x (isqrt n)) 2) n)))

(defun ferma (numb)
    (if (= 0.0 (rem numb (sqrt numb)))
        (cons (sqrt numb) (sqrt numb))
    (loop named test
        for x from 1 to MOST-POSITIVE-FIXNUM
        when (= 0.0 (rem (myfun x numb) 1))
        do (return-from test (cons
            (round (- (+ (isqrt numb) x) (myfun x numb)))
            (round (+ (+ (isqrt numb) x) (myfun x numb)))
        )))))

(defun fferma (numb)
    (if (= numb (cdr (ferma numb)))
        numb
        (list (fferma (car (ferma numb))) (fferma (cdr (ferma numb))))
        ))