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A008982 Number of immersions of the oriented circle into the unoriented plane with n double points. 6
1, 2, 5, 21, 102, 640, 4492, 34047, 272252, 2268085, 19502386, 172113886, 1551948268 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

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.

S. M. Gusein-Zade and F. S. Duzhin, On the number of topological types of plane curves; (Russian) Uspekhi Mat. Nauk 53 (1998), number 3(321), 197-198. English translation: Russian Mathematical Surveys 53 (1998) 626-627.

CROSSREFS

Cf. A008980, A008981, A008983, A008984, A008985, A054993.

Sequence in context: A270597 A115087 A008981 * A185134 A130471 A002628

Adjacent sequences:  A008979 A008980 A008981 * A008983 A008984 A008985

KEYWORD

nonn,nice

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 24 23:45 EDT 2020. Contains 334581 sequences. (Running on oeis4.)