The total amount of bitcoin in circulation decreased by almost 9 in 2017 due to “burn” addresses. Burn addresses, like the Genesis Block, are deadlier than “zomby” addresses, because there is no chance of coming back once BTC is sent to it. There are almost 400 known bitcoin burn addresses, i.e. valid addresses with no private key, to which, for a variety of reasons, people have sent 2,759.42507135 over the years. In 2017, 9 of these addresses received 8.97140133 BTC.


http://bitcoinwhoswho.com/blog/2017/12/30/8-97-bitcoins-burned-in-2017/