The centerpiece of Prince’s most exhilarating 21st-century album is “Black Sweat,” a spare, bass-less electronic drum track overlaid with whining synths that slams like a grittier revamp of “Kiss,” or maybe the missing link between James Brown and mid-2000s Oakland rap. Whether effortlessly seducing with the humid ballad “Te Amo Corazón,” playfully rejecting a young woman’s advances on “Lolita,” or launching into a psychedelic guitar workout on “Fury,” Prince didn’t so much cover new ground on 3121 as demonstrate that his home turf remained an inexhaustible source of inspiration. He hadn’t sounded so contemporary—or timeless—in years.