dickbutt

(defun triangle (x)
    (if (stringp x)
        (progn
            (write-line (concatenate 'string "(triangle " (write-to-string x) ") please enter an odd integer"))
            (return-from triangle 0)
        )
    )
    (if (= (mod x 2) 0)
        (progn
            (write-line (concatenate 'string "(triangle " (write-to-string x) ") even numbers are not valid input, please enter an odd integer"))
            (return-from triangle 0)
        )
    )
    (if (< (mod x 2) 1)
        (progn
            (write-line (concatenate 'string "(triangle " (write-to-string x) ") decimal numbers are not valid input, please enter an odd integer"))
            (return-from triangle 0)
        )
    )

    (setq str "1")
    (write-line str)
    (loop for i from 1 to (+ (/ x 2) 1) do
        ;; (print (format t "~d" i))
        (setq ci (+ (* i 2) 1))
        (setq str (concatenate 'string str " " (write-to-string ci)))
        (write-line str)
    )
    (write-line "-----")
)


(triangle 7)
(triangle 9)
(triangle 23)
(triangle 2.5)
(triangle 4)
(triangle "4")