Project Euler 25

1000-digit Fibonacci number

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?

就是一个斐波拉契数列数列……

直接上代码：

# coding utf-8
# Desc : Project Euler Problem 19 Fibonacci number
# Date : 2015-12-23
# Author : Tina

def fibonacci(n):
fac1 = 1
fac2 = 1
for x in xrange(2,n):
tmp = fac2
fac2 = fac1+fac2
fac1 = tmp
return fac2

n = 1
i = 5
while(n<1000):
x = fibonacci(i)
n = len(str(x))
i = i+1
print i-1