I was trying to think of something different for a montage and came up with the idea of '36 Things'.
A montage of 36 images laid out in a 6x6 grid, all the images would be linked by a theme. The theme can be anything at all, colour, location, subject, time or whatever.
Also 36 seems to be a reasonable number. Fits in an A4 or A3 print and gives a reasonable size of image, it can be made landscape or portrait format. It also has a resonance back to the days of film with 36 images being the length of 35mm film that was sold.