1,1
The hexagonal lattice is the familiar 2-dimensional lattice in which each point has 6 neighbors. This is sometimes called the triangular lattice.
J. Blease, Series expansions for the directed-bond percolation problem, J. Phys. C 10 (1977), 917-924.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
G. Nebe and N. J. A. Sloane, Home page for hexagonal (or triangular) lattice A2
Sequence in context: A014286 A000714 A090984 * A056823 A105544 A119917
Adjacent sequences: A006810 A006811 A006812 * A006814 A006815 A006816
nonn
N. J. A. Sloane (njas(AT)research.att.com).
