Lake

A lake is a still life that is a simple closed curve made from diagonally connected dominoes. The smallest example is the pond and the next smallest is lake 2. The seven smallest lakes are shown below. The number of cells in a lake is always divisible by 8, and for any multiple of 8 other than 16 there is a lake with that many cells. The number of distinct lakes with 8n cells for n = 1, 2, 3, ... is given by the sequence 1, 0, 1, 1, 4, 7, 31, 98, 446, 1894, 9049, 43151, ... (Sloane's A156228).