3,4

These are called simple arrangements.

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. 6.

Cf. A003036, A048872.

Sequence in context: A102958 A085649 A152396 this_sequence A091390 A132150 A091389

Adjacent sequences: A048870 A048871 A048872 this_sequence A048874 A048875 A048876

nonn,nice,more

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

The next term is conjectured to be 135.