Nitpick: you mean A4. As an aside to those who don’t get to use ISO A paper sizes, they are trés cool. The x/y edge sizes are the (edit) square root of two. A0 is 1 square metre in area. Each step (A1, A2, A3, ...) just chops the sheet in half.
As an aside, there are also ISO B and C series paper, although I believe that the C standard was withdrawn somewhat recently. The area of B_n is the geometric mean of that of A_n and A_{n-1}, while the area of C_n is the geometric mean of that of A_n and B_n. Without context, C4 paper sounds quite scary, until you realize it's probably related to A4 paper in some way. As to why it isn't just called A3.75, I have no idea.
Shoot, missed the edit window. Thanks for the heads up, though.