Euler Project 92

A number chain is created by continuously adding the square of the digits in a number to form a new number until it has been seen before.

For example,

44  32  13  10  1  1
85  89  145  42  20  4  16  37  58  89

Therefore any chain that arrives at 1 or 89 will become stuck in an endless loop. What is most amazing is that EVERY starting number will eventually arrive at 1 or 89.

How many starting numbers below ten million will arrive at 89?

My Solution

(defun squartsum(n)

  (let ((numberstr (format nil "~a" n)))

    (loop for i from 0 to (- (length numberstr) 1)

            sum (expt (parse-integer numberstr :start i :end (+ i 1)) 2))))

(defun IsEnd89(n)

  (let ((currentstage (squartsum n)))

    (loop

      (if (= 89 currentstage)

          (return T)

         (if (= 1 currentstage)

             (return nil)

             (setq currentstage (squartsum currentstage)))))))

(defun Euler(n)

  (let ((numberof89 0))

    (loop for j from 1 to n

          do(if (IsEnd89 j)

                  (progn (print j) (incf numberof89))))

    numberof89))