The problem is that you are reversing the string a few times. The following will do: (defun base8 (n) (let ((t8 (truncate n 8)) (m8 (mod n 8))) (if (= t8 0) (list m8) (append (base8 t8) (list m8))))) EDIT Here's a solution without append, using a helper function.
On average, a kidney weighs approximately 150 to 160 grams and, together, both kidneys weigh about 0.5 percent of total body weight. Usually, the left kidney is slightly larger than the right. These measurements and weights represent the typical ranges of a healthy, adult human kidney.
In adult males, the kidney weighs between 125 and 170 grams. In females the weight of the kidney is between 115 and 155 grams. A Danish study measured the median renal length to be 11.2 cm (4.4 in) on the left side and 10.9 cm (4.3 in) on the right side in adults. Median renal volumes were 146 cm3 on the left and 134 cm3 on the right.