Do you need a specific birthday candle?? Usually you can only find the numbers that you don't need (Murphy's Law)?
Here's your solution. You can use the typical thin candles with a customized number as the base.
If you want to print directly the .stl, it's ready to do it (candle diameter: 5.6-5.7 mm)
But if you need to change something (as the diameter, the size or the base position) make sure you follow these steps:
Enjoy it!!! I did it! (Today it's my birthday! ^^ So I printed them, and they work perfectly.)
I made the code in C++, using the new realased OOML 2.0 library (http://www.thingiverse.com/thing:17761 iearobotics.com/oomlwiki). So, If you want to change some of the parameters (dimensions) or work with this code to make some derivated or new desings, you should download this libray. Afterwards, you only have to open the .cpp and change it.
I also add the OpenScad generated code; however, I think it isn't very intuitive to change.