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A048873 Number of non-isomorphic arrangements of n lines in the real projective plane such that the lines do not pass through a common point and no point belongs to more than 2 lines. 5
1, 1, 1, 4, 11 (list; graph; refs; listen; history; text; internal format)
OFFSET

3,4

COMMENTS

These are called simple arrangements.

REFERENCES

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

B. Gr├╝nbaum, Arrangements and Spreads. American Mathematical Society, Providence, RI, 1972, p. 6.

LINKS

Table of n, a(n) for n=3..7.

CROSSREFS

Cf. A003036, A048872.

Sequence in context: A152396 A326720 A307491 * A091390 A321967 A230024

Adjacent sequences:  A048870 A048871 A048872 * A048874 A048875 A048876

KEYWORD

nonn,nice,more

AUTHOR

N. J. A. Sloane

EXTENSIONS

The next term is conjectured to be 135.

STATUS

approved

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Last modified December 11 23:44 EST 2019. Contains 329945 sequences. (Running on oeis4.)