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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: A299880 A085649 A152396 * 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 January 21 13:28 EST 2019. Contains 319350 sequences. (Running on oeis4.)