Re: [alexandria-devel] Subfactorial is wrong starting from 11

Here is a correct, linear-time implementation of subfactorial:

(defun subfactorial (n) "Subfactorial of the non-negative integer N." (check-type n (integer 0)) (if (zerop n) 1 (do ((x 1 (1+ x)) (a 0 (* x (+ a b))) (b 1 a)) ((= n x) a))))

and the corresponding test

(deftest subfactorial.1 (mapcar #'subfactorial (iota 22)) (1 0 1 2 9 44 265 1854 14833 133496 1334961 14684570 176214841 2290792932 32071101049 481066515734 7697064251745 130850092279664 2355301661033953 44750731559645106 895014631192902121 18795307255050944540)).