The crossing number of is the minimum number of crossings in all drawings of in the plane.

The -dimensional (hyper)cube is the graph whose vertices are all binary sequences of length , and two of the sequences are adjacent in if they differ in precisely one coordinate.

**Conjecture**

It is known that for and that . No other exact values are known. Madej [M] proved that . Faria and de Figueiredo [FF] improved the upper bound to . Sykora and Vrto [SV] proved that is a lower bound on .

## Bibliography

*[EG] P. Erdős and R.K. Guy, Crossing number problems, Amer. Math. Monthly 80 (1973) 52-58.

[FF] L. Faria, C.M.H. de Figueiredo, On Eggleton and Guy's conjectured upper bound for the crossing number of the -cube, Math. Slovaca 50 (2000) 271-287.

[M] T. Madej, Bounds for the crossing number of the -cube, J. Graph Theory 15 (1991) 81-97.

[SV] O. Sykora and I. Vrto, On crossing numbers of hypercubes and cube connected cycles, BIT 33 (1993) 232-237.

* indicates original appearance(s) of problem.