A008982 - OEIS

%I #13 Apr 19 2018 17:00:43

%S 1,2,5,21,102,640,4492,34047,272252,2268085,19502386,172113886,

%T 1551948268

%N Number of immersions of the oriented circle into the unoriented plane with n double points.

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

%H S. M. Gusein-Zade and F. S. Duzhin, <a href="http://www.botik.ru/~duzhin/as/dataprog/">On the number of topological types of plane curves</a>; (Russian) Uspekhi Mat. Nauk 53 (1998), number 3(321), 197-198. English translation: Russian Mathematical Surveys 53 (1998) 626-627.

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

%K nonn,nice

%O 0,2

%A _N. J. A. Sloane_

%E Additional comments from _Sergei Duzhin_, Nov 11 2000

%E a(11)-a(12) from _Sean A. Irvine_, Apr 19 2018