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%I #53 Mar 30 2024 12:15:26
%S 1,1,2,6,21,99,588,3829,27404,206543,1626638,13242275,110865868,
%T 950078474,8307074080,73908443799,667684486429
%N Number of immersions of an unoriented circle into the oriented sphere with n double points.
%D V. I. Arnold, Topological Invariants of Plane Curves and Caustics, American Math. Soc., 1994, p. 18.
%H R. Coquereaux and J.-B. Zuber, <a href="http://arxiv.org/abs/1507.03163">Maps, immersions and permutations</a>, arXiv preprint arXiv:1507.03163 [math.CO], 2015-2016. Also J. Knot Theory Ramifications 25, 1650047 (2016), DOI: <a href="https://doi.org/10.1142/S0218216516500474">10.1142/S0218216516500474</a>.
%H Guy Valette, <a href="https://doi.org/10.1007/s40598-016-0049-3">A Classification of Spherical Curves Based on Gauss Diagrams</a>, Arnold Math J. (2016) 2:383-405.
%o (Magma) // see A260848
%Y Cf. A008986, A008988, A008989. First line of triangle A260848.
%K nonn,more
%O 0,3
%A _N. J. A. Sloane_
%E a(6)-a(7) from _Guy Valette_, Feb 09 2004
%E a(8)-a(9) from _Robert Coquereaux_ and Jean-Bernard Zuber, Jul 21 2015
%E a(10) from same source added by _N. J. A. Sloane_, Mar 03 2016
%E a(11)-a(14) from _Brendan McKay_, Mar 11 2023
%E a(15)-a(16) from _Brendan McKay_, Mar 29 2024
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