Plane division by ellipses is the partition of the plane into regions by an arrangement of ellipses, where
is a nonnegative integer.
For
,
the maximal number of regions is
giving values for , 2, ... of 2, 6, 14, 26, 42, 62, 86, 114, ... (OEIS A051890).
The maximum is attained when each pair of ellipses intersects in four distinct points
and no three ellipses pass through the same point.
For ,
the
th
ellipse then adds
regions. With no ellipses,
.