I found a typo in the Sage documentation, at the function period():
http://doc.sagemath.org/html/en/reference/rings_standard/sage/rings/rational.html#sage.rings.rational.Rational.period
It should be "In general if d=2^a5^bm where m is coprime to 10" instead of "In general if d=2^a3^bm where m is coprime to 10".