a(n) is also the number of walks of length 4*n on a 2D lattice with the properties that: it turns 90 degrees after every step of length 1, it is a closed loop (ie. it ends where it started) and it never crosses itself.
Table of n, a(n) for n=1..12.
N. Johnston, Counting Lakes
a(2) = 0 because there are no lakes with 16 cells.
Sequence in context: A080871 A102666 A123801 * A218959 A283332 A000289
Adjacent sequences: A156225 A156226 A156227 * A156229 A156230 A156231
Nathaniel Johnston, Feb 06 2009
a(11) and a(12) added by Nathaniel Johnston, Mar 09 2009