Wikipedia is one source where the value 9550 is rounded slightly from what is documented on Wikipedia per below as 9,554.
The below copy and paste is better viewed from website, but if you take the following constants in the formula
60,000 / 2 * Pi
60,000 / 2 * 3.14
Conversion to other units
A conversion factor may be necessary when using different units of power, torque, or angular speed. For example, if rotational speed (revolutions per time) is used in place of angular speed (radians per time), we multiply by a factor of 2π radians per revolution.
Dividing on the left by 60 seconds per minute and by 1000 watts per kilowatt gives us the following.
where rotational speed is in revolutions per minute (rpm).
Some people (e.g. American automotive engineers) use horsepower (imperial mechanical) for power, foot-pounds (lbf·ft) for torque and rpm for rotational speed. This results in the formula changing to:
The constant below in, ft·lbf/min, changes with the definition of the horsepower; for example, using metric horsepower, it becomes ~32,550.
Use of other units (e.g. BTU/h for power) would require a different custom conversion factor.