Question 25 from Project Euler:

The Fibonacci sequence is defined by the recurrence relation: Fn = Fn1 + Fn2, 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 Fibonacci sequence to contain 1000 digits?

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2
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19

import time
start = time.time()
 
length = 0 ; x = 1 ; y = 2 ; n = z = 3
#y = previous term
#x is the term before that
#z = current term
#use n to count terms
while length < 1000:
    #create new term
    #reassign old values
    #set length
    z = x+y
    x, y = y, z
    length = len(str(z))
    n += 1
print n
 
print time.time()-start