There have been several milestones in the Paralympic movement. The first official Paralympic Games, no longer open solely to war veterans, was held in Rome in 1960 Summer Paralympics. 400 athletes from 23 countries competed at the 1960 Games. Since 1960, the Paralympic Games have taken place in the same year as the Olympic Games. The Games were initially open only to athletes in wheelchairs; at the 1976 Summer Paralympics, athletes with different disabilities were included for the first time at a Summer Paralympics. With the inclusion of more disability classifications the 1976 Summer Games expanded to 1,600 athletes from 40 countries. The 1988 Summer Paralympics in Seoul, South Korea, was another milestone for the Paralympic movement. It was in Seoul that the Paralympic Summer Games were held directly after the 1988 Summer Olympics, in the same host city, and using the same facilities.  This set a precedent that was followed in 1992 Summer Paralympics, 1996 Summer Paralympics and 2000 Summer Paralympics. It was eventually formalized in an agreement between the International Paralympic Committee (IPC) and the International Olympic Committee (IOC) in 2001, and was extended through 2020. On March 10, 2018, the two committees further extended their contract to 2032. The 1992 Winter Paralympics were the first Winter Games to use the same facilities as the 1992 Winter Olympics.
Question: How many more countries competed in the Paralympic Games in 1976 than in 1960?
Answer: 17