Are they a boy band or a small militia? Even for K-pop, a genre known for its large ensembles, SEVENTEEN’s size is big: 13 full-time members vie for space on each track — and in each video. But that surfeit of talent isn’t a weakness. If anything, it’s made this cheerful, shambling group insanely productive and versatile. Since their 2015 debut, they’ve released a small tsunami of EPs and a handful of LPs, and the members have become a driving force creatively. Their biggest inspiration? The urbane but still appropriate sounds of ’90s hip-hop and R&B. These guys swagger, but underneath that toughness, they love a good pop hook, which makes them extremely fun to see live.