Tileset Animations Limited to Powers of 2?

Started playing with tilesets last night and noticed the number of frames in your animations is limited to powers of 2 in the drop box. Is there are reason why this is the case? Are there any easy workarounds if you have a 3-frame tiled animation? Trying to replicate some old game imagery and it all runs on 3-frame cycles, and I've done animated objects before but this would literally be hundreds and hundreds of objects to place.