I’ve now completed 5 problems.  None of them as efficient as I could have, but these are still the early days.  The last problem I completed was finding the sum of the digits of 100!.  For some reason, it gave me a great feeling when I completed this one.  It may be that I’m beginning to feel a bit better using Lisp or maybe that I’m not running in to as many road blocks as I was even yesterday, I dunno.  Anyway, to show it off, I’ll post the code to my ‘not-so-efficient’ answer to problem 20:

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(defun fac (n)
  (if (<= n 1)
      '1
    (apply #'* (loop for i from 1 to n collect i))))
 
(defun euler-problem-020 ()
  (let ((string-version "")
        (ch nil)
        (sum 0))
    (setf string-version (princ-to-string (fac 100)))
    (loop for i from 0 below (length string-version) do
          (setf ch (char string-version i))
          (setf sum (+ sum (parse-integer (princ-to-string ch)))))
    sum))