Question: Pentatonix, the five-member American a cappella group lost their vocalist Avi Kaplan in 2017 at the same time as their tribute to which group received over 250 million views?
Sentence (from "Pentatonix"): With over 13 million subscribers and 2.4 billion views, Pentatonix's YouTube channel is currently the 50th most-subscribed YouTube channel.
Relevant evidence: Yes