How to match numbers ranging from 400 to 550 with regex?

I want to validate a numeric string that must only contain numbers ranging from 400 to 550.

$x = "401";  // valid 
$x = "551";  // invalid 

I want to only match the numbers between 400 and 550.

I tried the following pattern:


But it doesn't work.

What is the regex pattern for matching numbers 400-550?


A regex-way to validate this range:


See demo. It will also work in larger texts since \b boundaries are used. In case of whole strings, use ^ and $ around instead of \b.

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