Table of n, a(n) for n=1..10.
a(4)=1 because there is only one still-life with four cells: the tub (four cells bordering all four sides of an empty spot).
Cf. A019473, A166476, A175000
Sequence in context: A064848 A333335 A212791 * A205843 A171727 A171942
Adjacent sequences: A174998 A174999 A175000 * A175002 A175003 A175004
Christian Schroeder, Apr 03 2010