The Lancret equation relates the normal, tangent, and binormal line elements of a space curve. Let a space curve have line elements , , and along the normal, tangent, and binormal vectors respectively, then
where
and and are the curvature and torsion, respectively.
More things to try:
Weisstein, Eric W. "Lancret Equation." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/LancretEquation.html