source is CoinGlass on the numbers. Eventually they are gonna run out of fake bitcoin IOUs to print up out of thin air. There's only 1,843,794 bitcoin left to be mined and it looks like 657k got sold "pre-mined" (not that kind of pre-mine) via future contracts. Few acutally understand this.
Source and link to Reddit topic: There is only 2,093k BTC on exchanges, but there is 657k Bitcoin Futures Contracts on exchanges. effectively diluting the supply on exchanges by 31%. I think its these fake IOUs that have caused the number to go down.