I think it is closer to 9-10 times (on level asphalt road on a "normal" bike) although it heavily depends on some factors like speed, type of bike and your proficiency, terrain and type of ground.
Riding a bike is most efficient at a certain speed and becomes less efficient very quickly as you get faster. So when I mean 9-10 times more efficient, I mean a person walking at a comfortable speed vs cyclist riding at a comfortable speed (on relatively level asphalt road).
Riding a bike is most efficient at a certain speed and becomes less efficient very quickly as you get faster. So when I mean 9-10 times more efficient, I mean a person walking at a comfortable speed vs cyclist riding at a comfortable speed (on relatively level asphalt road).