Tube Puzzle

SPOTTED the following serial number on  a Circle Line carriage: 21497
As usual with these tube puzzles, each number should be used once, and once only, and must be added, subtracted, multiplied or divided to make a balanced equation.
There is a perfect solution, ie one that uses the digits in the order printed.
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My solution: 2 = 1 + 4 + 9 (÷ 7)