1,4

Also the number of polyominoes on n points, up to isomorphism of the adjacency graph.

Also the number of "grid graphs" (finite induced subgraphs of the integer lattice using only horizontal and vertical edges) on n vertices.

Table of n, a(n) for n=1..12.

P. C. Staecker, Some enumerations of binary digital images, arXiv 1502.06236 [math.CO], 2015.

Sequence in context: A139797 A306334 A036649 * A321197 A109887 A200981

Adjacent sequences: A255536 A255537 A255538 * A255540 A255541 A255542

nonn,more,hard

P. Christopher Staecker, Feb 24 2015

approved