because round numbers are for noobs

mike and steve have it right

they reflect the largest numbers you can get with binary (only 0 and 1 exist)
2 = 1
4 = 11
6 = 111
8 = 1111
16 = 11111
number of combinations of 1 and 0 = number of digits you can put next to each other

keep adding another 1, you'll multiply the largest number by 2

yeah my answer is probably as incoherant as that old geezer over there *points to steve*
but i'm also getting old and senile... that and i expect everyone to know what binary is and so what i said makes sense...

ps, programmer's worst nightmare: 011011012