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A008981 Number of immersions of the unoriented circle into the oriented plane with n double points. 6
1, 2, 5, 21, 102, 639, 4492, 34032, 272252, 2267905, 19502386, 172111844, 1551948268 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

See Table 1, column 3 of E. D. Demaine et al. paper. - Parthasarathy Nambi, Jan 22 2010

REFERENCES

V. I. Arnold, Topological Invariants of Plane Curves and Caustics, American Math. Soc., 1994, p. 16.

LINKS

Table of n, a(n) for n=0..12.

E. D. Demaine, M. L. Demaine, P. Taslakian and G. T. Toussaint, Sand drawings and Gaussian graphs, Journal of Mathematics and the Arts, 1 (2007), 125-133.

S. M. Gusein-Zade and F. S. Duzhin, On the number of topological types of plane curves; (Russian) Uspekhi Mat. Nauk 53 (1998), no. 3(321), 197-198. English translation: Russian Mathematical Surveys 53 (1998) 626-627.

S. M. Gusein-Zade and F. S. Duzhin, Enumeration of plane curves with up to 10 selfintersections, Pascal program and result table, 05 Apr 1998.

PROG

(Pascal) Cf. link.

CROSSREFS

Cf. A008980, A008982, A008983, A008984, A008985, A054993.

Cf. A172023. - Parthasarathy Nambi, Jan 22 2010

Sequence in context: A319850 A270597 A115087 * A008982 A185134 A130471

Adjacent sequences:  A008978 A008979 A008980 * A008982 A008983 A008984

KEYWORD

nonn,nice,hard,more

AUTHOR

N. J. A. Sloane

EXTENSIONS

Additional comments from Sergei Duzhin, Nov 11 2000

a(11)-a(12) from Sean A. Irvine, Apr 19 2018

STATUS

approved

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Last modified May 25 06:42 EDT 2020. Contains 334581 sequences. (Running on oeis4.)