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 index of the first term in the Fibonacci sequence to contain 1000 digits?

def fib_gen():
    index = 1
    cur = 1
    past = 0
    while True:
        yield [index,cur]  
        old = cur
        cur = cur + past
        past = old
        index +=1
      

def solve25():
    solved = False
    s = fib_gen()
    while not solved:
        current_fib = next(s)
        digits = len(str(current_fib[1]))
        if digits>999:
            print current_fib[0]
#             solved = True
            break

solve25()

4782