Project Euler #64

64.py

#!/usr/bin/env python

def period(n):
    a_0 = int(n ** 0.5)
    if a_0 * a_0 == n:
        return 0
    b, b_0 = a_0, a_0
    c, c_0 = n - a_0*a_0, n - a_0*a_0
    res = 0
    while True:
        a = (a_0 + b) / c
        b = a * c - b
        c = (n - b * b) / c
        res += 1
        if b == b_0 and c == c_0:
            break
    return res

if __name__ == '__main__':
    print sum(
        map(lambda n: period(n) % 2, 
            xrange(2, 10001)))