How dense is the atmosphere between 100 km and geosynch orbit at 36,000 km?

The density drops to about 500,000 atoms per cc at 300 km and by 1000 km you enter the exosphere where atoms are lost from the earth completely so that by geosynchronous orbit, there is no earth atmosphere at all and instead you are in the magnetosphere with its trapped high energy particles that it gains from the solar wind at densities of 2 - 50 per cc depending on the level of solar activity.