Pictures are always a big help. Serial number on the frame, either under the cylinder crane or on the bottom of the grip frame. Depending on the grips, they can cover the number on the bottom of the grip frame at times. Your c-21 is not it.
Your question is like "I have a car, what make and model is it?" You have provided no info to go on.
Open the cylinder. Is there a model number stamped there? Looks like this...
The above revolver happens to have the serial stamped above the model number. Often they do not. Look at the butt for the serial...
What you gave was an assembly number. Mention any letters as they are a part of the serial (see the N on the one above). If the gun was made before 1957 there will not be a model number. But the serial will tell us what it is.
Does it have adjustable sites or just a groove in the top of the frame? Is the ejector rod under the barrel exposed or is it covered by a shroud? The correct serial will actually tell all we need to know.