If the focal length, minor axis length and major axis length of an ellipse form an arithmetic sequence, then the eccentricity is______ .

If the focal length, minor axis length and major axis length of an ellipse form an arithmetic sequence, then the eccentricity is______ .

According to the meaning of the question, the focal length, the length of the minor axis and the length of the major axis of the ellipse form a sequence of arithmetic numbers, and the answer is: 35