Upon raising the landing gear after takeoff, the gear motor continued to operate longer than normal, and the pilot heard an abnormal sound toward the end of the sequence. The right main gear was hanging at about a 45-degree angle, and the left main gear was not visible. The pilot completed the appropriate checklists, without change. The pilot declared an emergency and ATC confirmed during a fly-by that the main gear was not extended. During the landing, the nose gear remained extended and the two main gear were retracted. The airplane came to rest on the runway and the passengers egressed without further incident.