On Minimal-Perimeter Lattice Animals

A lattice animal is a connected set of cells on a lattice. The perimeter of a lattice animal A consists of all the cells that do not belong to A, but that have a least one neighboring cell of A. We consider minimal-perimeter lattice animals, that is, animals whose periemeter is minimal for all animals of the same area, and provide a set of conditions that are sufficient for a lattice to have the property that inflating all minimal-perimeter animals of a certain size yields (without repetitions) all minimal-perimeter animals of a new, larger size. We demonstrate this result for polyhexes (animals on the two-dimensional hexagonal lattice). In addition, we provide two efficient algorithms for counting minimal-perimeter polyhexes.

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