4,1

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

S. G. Whittington and J. P. Valleau, Figure eights on the square lattice: enumeration and Monte Carlo estimation, J. Phys. A 3 (1970), 21-27.

Sequence in context: A071007 A027617 A154626 this_sequence A076625 A139415 A119817

Adjacent sequences: A003302 A003303 A003304 this_sequence A003306 A003307 A003308

nonn

N. J. A. Sloane (njas(AT)research.att.com).