Use only a single hash character (ex., compName_[#].png). After Effects will continue to add the appropriate number of digits as necessary; the hash characters only define how many leading zeroes are written.
Remember that you can also save your custom output names as a template.
You really don't want to do that. It can foul up the frame order because in many applications image sequences need the leading zeros. You can end up with a sequence like this
and so on. It's not a wise workflow. AE will, most of the time, make it work, but fixing a few frames or multi machine rendering can get awfully fouled up if your frame numbers do not contain leading zeros... The leading zeros will never foul anything up, leaving them out often does.
That's what batch renaming tools are for of which you can find about a quadrillion on the Internet. I wouldn't bother with any of this trying to make AE do something it doesn't want.
FYI, Apple Watch OS doesn't like the leading zeros when compiling animation sequences from a set of PNGs. So it is a problem, but the original reply I believe fixes it