3,4

J. E. Goodman and J. O'Rourke, editors, Handbook of Discrete and Computational Geometry, CRC Press, 1997, p. 102.

B. Gr\"{u}nbaum, Arrangements and Spreads. American Mathematical Society, Providence, RI, 1972, p. 7.

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

Cf. A048872, A048873.

Sequence in context: A084718 A154851 A037445 this_sequence A089818 A067025 A049047

Adjacent sequences: A003033 A003034 A003035 this_sequence A003037 A003038 A003039

nonn,nice

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