Missing Jacket

Roger and Rafael visited a small town in France. While coming back , Roger forgot his Jacket in a bus. When he reported this to the bus company, the company asked him the bus number , which he vaguely remembered but he noted a peculiar property of the bus number. The number plate showed that the bus number was a perfect square and also if the plate was turned upside down, the number would still be perfect square. The bus company informed him they had only 500 buses with numbers from 1 to 500 . How was Roger able to deduce the bus number and what was the bus number ?