This thread fascinates me! I always wondered if anyone has this problem and now I know it's a common OCD behaviour.
My favourite number ever since early childhood is 4! I find it very even and symmetrical.
Most multiples of 4 is fine (unless it is also a multiple of 7 ... loses that symmetry I guess)
Off the top of my head, going through the numbers 1 to 100 these are the numbers I like (or can tolerate):
2, 4, 8, 12, 16, 20, 24, 32, 36, 40, 48, 64, 72, 80, 84, 96, 100
4 and 16 are my favourite. If something has a scale of 1 to 100 (e.g. TV volume) then I'm also happy with 25, 50, and 75 since they are quartiles of 100
I'm really glad it's a low number, makes things easy for number of times I have to do things. However if I have to do something a fifth time (e.g. I clear my throat 4 times but find that it's still not "clear") then I have to do repeat it until I hit 16 (i.e. 4 x 4) times.