1,5

S. A. Burr, in The Mathematical Gardner, Ed. D. A. Klarner, p. 94, Wadsworth, 1981.

S. A. Burr, B. Gr\"{u}nbaum and N. J. A. Sloane, The Orchard Problem, Geometriae Dedicata, 2 (1974), 397-424.

H. E. Dudeney, Amusements in Mathematics, Nelson, London, 1917, page 56.

M. Gardner, Time Travel and Other Mathematical Bewilderments. Freeman, NY, 1988, Chap. 22.

B. Gr\"{u}nbaum, Arrangements and Spreads. American Mathematical Society, Providence, RI, 1972, p. 22.

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

S. A. Burr, B. Gr\"{u}nbaum and N. J. A. Sloane, The Orchard Problem, Geometriae Dedicata, 2 (1974), 397-424.

N. J. A. Sloane, Illustration of initial terms (from Gruenbaum-Burr-Sloane paper)

Eric Weisstein's World of Mathematics, Link to a section of The World of Mathematics.

Link to the result [From Du, Zhao Hui (zhao.hui.du(AT)gmail.com), Nov 20 2008]

Cf. A006065, A008997, A058212.

Sequence in context: A047510 A071260 A026407 this_sequence A094453 A026398 A070119

Adjacent sequences: A003032 A003033 A003034 this_sequence A003036 A003037 A003038

nonn,nice,hard

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

13 and 14 trees result from Du, Zhao Hui (zhao.hui.du(AT)gmail.com), Nov 20 2008