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A008987
Number of immersions of an unoriented circle into the oriented sphere with n double points.
14
1, 1, 2, 6, 21, 99, 588, 3829, 27404, 206543, 1626638, 13242275, 110865868, 950078474, 8307074080, 73908443799, 667684486429
OFFSET
0,3
REFERENCES
V. I. Arnold, Topological Invariants of Plane Curves and Caustics, American Math. Soc., 1994, p. 18.
LINKS
R. Coquereaux and J.-B. Zuber, Maps, immersions and permutations, arXiv preprint arXiv:1507.03163 [math.CO], 2015-2016. Also J. Knot Theory Ramifications 25, 1650047 (2016), DOI: 10.1142/S0218216516500474.
Guy Valette, A Classification of Spherical Curves Based on Gauss Diagrams, Arnold Math J. (2016) 2:383-405.
PROG
(Magma) // see A260848
CROSSREFS
Cf. A008986, A008988, A008989. First line of triangle A260848.
Sequence in context: A008988 A061232 A020091 * A375132 A079129 A305923
KEYWORD
nonn,more
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
a(11)-a(14) from Brendan McKay, Mar 11 2023
a(15)-a(16) from Brendan McKay, Mar 29 2024
STATUS
approved