  Project Euler - Problem 25

;;The Fibonacci sequence is defined by the recurrence relation:

      Fn = Fn−1 + Fn−2 , where F1 = 1 and F2 = 1 .

  Hence the first 12 terms will be :

      F1 = 1
      F2 = 1
      F3 = 2
      F4 = 3
      F5 = 5
      F6 = 8
      F7 = 13
      F8 = 21
      F9 = 34
      F10 = 55
      F11 = 89
      F12 = 144

  The 12th term , F12 , is the first term to contain three digits .

  What is the first term in the  sequence to contain 1000
;; digits?

(defun euler-25 ()
  (loop with a = 0 and b = 1
     for i upfrom 2
     do (shiftf a b (+ a b))
     when (>= b (expt 10 999)) return i))

The Fibonacci sequence is defined by the recurrence relation:
 digits?
  Project Euler - Problem 25


      Fn = Fn−1 + Fn−2 , where F1 = 1 and F2 = 1 .

  Hence the first 12 terms will be :

      F1 = 1
      F2 = 1
      F3 = 2
      F4 = 3
      F5 = 5
      F6 = 8
      F7 = 13
      F8 = 21
      F9 = 34
      F10 = 55
      F11 = 89
      F12 = 144

  The 12th term , F12 , is the first term to contain three digits .

  What is the first term in the  sequence to contain 1000

(defun euler-25 ()
  (loop with a = 0 and b = 1
     for i upfrom 2
     do (shiftf a b (+ a b))
     when (>= b (expt 10 999)) return i))
