A numerical knot invariant. For a tame knot 
,
the bridge index is the least bridge number of all
planar representations of the knot. The bridge index of
the unknot is defined as 1.
Bridge Index
See also
Bridge Number, CrookednessExplore with Wolfram|Alpha
References
Rolfsen, D. Knots and Links. Wilmington, DE: Publish or Perish Press, p. 114, 1976.Schubert, H. "Über eine numerische Knotteninvariante." Math. Z. 61, 245-288, 1954.Referenced on Wolfram|Alpha
Bridge IndexCite this as:
Weisstein, Eric W. "Bridge Index." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/BridgeIndex.html