Three Dog Night has always been an anomaly in the music world. In 1968, the seven-man hit-making machine with the weird name (it’s an Aboriginal expression) hit the scene with three lead singers and a cache of catchy songs written by then-under-the-radar songwriters (including Elton John, Harry Nilsson, Robbie Robertson, and Laura Nyro). They weren’t especially cool, yet they filled stadiums, earned 14 gold albums, had 21 top-40 singles, and sold more than 40 million records in less than a decade. If you’re among the 40 million who bought “Joy to the World,” “Shambala,” “Eli’s Comin’,” “Never Been to Spain,” “One (is the Loneliest Number),” or “Mama Told Me (Not to Come),” check them out when they perform on July 21 at Empire City Casino.