A264759 Number of irreducible indecomposable spherical curves with n crossings (only ordinary double points), the circle is not oriented, the sphere is not oriented (UU case).

0, 0, 1, 1, 2, 3, 10, 27, 101, 364, 1610, 7202, 34659, 170692, 864590, 4463287, 23415443, 124526110, 670224294, 3644907768, 20011145443, 110794212315, 618187581204

Offset: 1

Author

Robert Coquereaux, Nov 23 2015

Keywords

• nonn
• more

Comments

Irreducible means not made disconnected by removal of a vertex (no nugatory crossings).

Indecomposable (or prime) means not made disconnected by cutting two disjoint lines.

From Robert Coquereaux and Andrey Zabolotskiy, Nov 30 2021: (Start)

Equivalently, the number of projections of prime alternating knots with n crossings, or prime knot shadows.

This sequence up to n = 10 was known to Kirkman (1885) and confirmed by Little (1890). The terms up to n = 14 are given by Hoste et al. (1994) and independently found by J. Bétréma using his program.

A 1999 unpublished result by J. Hoste gives a(15) = 864127, a(16) = 4463287, a(17) = 23415443. J. Bétréma's program gives the same a(16) but different a(15) = 864590. (End)

Using plantri I find a(15) = 864590, agreeing with Bétréma. - Brendan McKay, Mar 13 2023

Links

• Brian Arnold, Michael Au, Christoper Candy, Kaan Erdener, James Fan, Richard Flynn, Robs John Muir, Danny Wu and Jim Hoste, Tabulating alternating knots through 14 crossings, Journal of Knot Theory and Its Ramifications, 3 (1994), 433-437. Gives the sequence up to n = 14.
• J. Betrema, Tait Curves
• Gunnar Brinkmann and Brendan McKay, plantri plane graph generator. To obtain this sequence use options -Guqc2m2d (which makes plane quartic graphs) and count those for which the straight-ahead Eulerian walk has a single component.
• Robert Coquereaux and Jean-Bernard Zuber, Maps, immersions and permutations, arXiv preprint arXiv:1507.03163 [math.CO], 2015-2016. Also J. Knot Theory Ramifications (2016) Vol. 25, No. 8, 1650047. Gives the sequence up to n = 10. The immersions for n = 8, 9 are shown in Figs. 15-17.
• Noboru Ito and Yusuke Takimura, The tabulation of prime knot projections with their mirror images up to eight double points, Topol. Proc. 53, 177-199 (2019). [The diagrams up to n = 8 are given in Table 4. Reference supplied by K. A. Perko, Jr., Jun 09 2019]
• Abdullah Khan, Alexei Lisitsa, Viktor Lopatkin and Alexei Vernitski, Circle graphs (chord interlacement graphs) of Gauss diagrams: Descriptions of realizable Gauss diagrams, algorithms, enumeration, arXiv:2108.02873 [math.GT], 2021.
• Abdullah Khan, Alexei Lisitsa, and Alexei Vernitski, Experimental Mathematics Approach to Gauss Diagrams Realizability, arXiv:2103.02102 [math.GT], 2021. Gives the sequence up to n = 13.
• Abdullah Khan, Alexei Lisitsa, and Alexei Vernitski, Gauss-Lintel, an Algorithm Suite for Exploring Chord Diagrams, Intelligent Computer Mathematics, Int'l Conf. Intel. Comp. Math. (CICM 2021), 197-202.
• T. P. Kirkman, The enumeration, description and construction of knots of fewer than ten crossings, Trans. Roy. Soc. Edinburgh 32 (1885), 281-309, doi:10.1017/S0080456800026788.
• Alexei Lisitsa and Alexei Vernitski, Counting graphs induced by Gauss diagrams and families of mutant alternating knots, Examples Counterex. (2024) Vol. 6, Art. No. 100162.
• C. N. Little, Alternate +/- knots of order eleven, Trans. Roy. Soc. Edinburgh 36 (1890), 253-255, doi:10.1017/S008045680003773X.
• P. G. Tait, On knots, Trans. Roy. Soc. Edin. 28 (1876/77), 145-190.

Crossrefs

Cf. A008986, A008987, A008988, A008989, A007756, A264760, A264761.

Programs

C

See the J. Betrema C program in the Tait Curves link.

Extensions

a(15)-a(21) from Brendan McKay, Mar 12 2023

Comment on link to plantri modified by Brendan McKay, Mar 25 2024

a(22) and a(23) from Brendan McKay, Mar 30 2024