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A008987 Number of immersions of unoriented circle into oriented sphere with n double points. 8
1, 1, 2, 6, 21, 99, 588, 3829, 27404, 206543, 1626638 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

a(10) = 1626638 by sampling method (to be confirmed; cf. ref. arXiv:1507.03163). - Robert Coquereaux, Nov 23 2015

REFERENCES

V. I. Arnold, Topological Invariants of Plane Curves and Caustics, American Math. Soc., 1994, p. 18.

Guy Valette, A Classification of Spherical Curves Based on Gauss Diagrams, Arnold Math J. (2016) 2:383-405, DOI 10.1007/s40598-016-0049-3.

LINKS

Table of n, a(n) for n=0..10.

R. Coquereaux, J.-B. Zuber, Maps, immersions and permutations, arXiv preprint arXiv:1507.03163 [math.CO], 2015. Also J. Knot Theory Ramifications 25, 1650047 (2016), DOI: http://dx.doi.org/10.1142/S0218216516500474

PROG

(MAGMA)  // see A260848

CROSSREFS

Cf. A008986, A008988, A008989. First line of triangle A260848.

Sequence in context: A008988 A061232 A020091 * A079129 A305923 A130275

Adjacent sequences:  A008984 A008985 A008986 * A008988 A008989 A008990

KEYWORD

nonn,more

AUTHOR

N. J. A. Sloane

EXTENSIONS

a(6)-a(7) from Guy Valette, Feb 09 2004

a(8)-a(9) from Robert Coquereaux and Jean-Bernard Zuber, Jul 21 2015

a(10) from same source added by N. J. A. Sloane, Mar 03 2016

STATUS

approved

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Last modified May 31 02:51 EDT 2020. Contains 334747 sequences. (Running on oeis4.)