OFFSET
1,2
COMMENTS
The hexagonal lattice is the familiar 2-dimensional lattice in which each point has 6 neighbors. This is sometimes called the triangular lattice.
REFERENCES
D. Dhar et al., Enumeration of directed site animals on two-dimensional lattices, J. Phys. A 15 (1982), L279-L284.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
LINKS
G. Nebe and N. J. A. Sloane, Home page for hexagonal (or triangular) lattice A2
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved