It was $22k on a few Korean exchanges 10 days ago, while all other exchanges sat at around $17k. This was likely that those exchanges didn't have enough BTC (not enough supply for the demand) and the performance of Bitcoin sucks for arbitrage. The differences in exchanges is probably going to get worse as Bitcoin degrades in confirmation times and fees.
You can see it in the graph on this exchange if you span it to 1 month:
https://www.bithumb.com/