A Brunnian link is a set of 
linked loops such that each proper sublink is trivial, so
that the removal of any component leaves a set of trivial unlinked unknots.
The Borromean rings are the simplest example and
have 
.
Brunnian Link
See also
Borromean RingsExplore with Wolfram|Alpha
References
Livingston, C. Knot Theory. Washington, DC: Math. Assoc. Amer., p. 10, 1993.Rolfsen, D. Knots and Links. Wilmington, DE: Publish or Perish Press, 1976.Referenced on Wolfram|Alpha
Brunnian LinkCite this as:
Weisstein, Eric W. "Brunnian Link." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/BrunnianLink.html