A287149 Number of arrangements of n circles in the affine plane having only one island or region, which is formed by the union of all solid circles of the arrangement.

1, 1, 2, 11, 155

Offset: 0

Author

Omar E. Pol, May 21 2017

Keywords

• nonn
• hard
• more

Comments

A subset of the arrangements of n circles described in A250001.

Note that a(4) = 155 does not include the arrangement of four circles in which there is a little circle that is surrounded by the union of three solid circles, because in that arrangement there are two islands or regions, not one.

Crossrefs

1 together with the first column of A252158.

First differs from A275923 at a(4).

Cf. A250001.