cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

A054993 Number of "long curves", i.e., topological types of smooth embeddings of the oriented real line into the oriented plane that coincide with the standard immersion x -> (x,0) in the neighborhood of -infinity and +infinity.

Original entry on oeis.org

1, 2, 8, 42, 260, 1796, 13396, 105706, 870772, 7420836, 65004584, 582521748, 5320936416, 49402687392, 465189744448, 4434492302426, 42731740126228, 415736458808868, 4079436831493480, 40338413922226212, 401652846850965808, 4024556509468827432, 40558226664529024000, 410887438338905738908, 4182776248940752113344, 42770152711524569532616, 439143340987014152920384, 4526179842103708969039296
Offset: 0

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Author

Sergei Duzhin, Nov 11 2000

Keywords

Comments

Also the number of knot diagrams with n crossings and two outgoing strings.

References

  • V. I. Arnold, Topological Invariants of Plane Curves and Caustics, American Math. Soc., 1994.
  • S. M. Gusein-Zade, On the enumeration of curves from infinity to infinity, in: Singularities and Bifurcations, Adv. Sov. Math., v. 21 (1994), pp. 189-198.

Crossrefs

A151374 enumerates the long curves having Gauss diagrams without intersections, cf. A118814.
A column of the triangles in A067640 and A062038.

Extensions

Extended to n = 22 by J. L. Jacobsen and Paul Zinn-Justin, Jan 30 2002
More terms from Paul Zinn-Justin, Dec 13 2016