Due to Euler's prolific output, there are a great number of theorems that are know by the name "Euler's theorem." A sampling of these are Euler's
displacement theorem for displacement of a rigid body with one point fixed, Euler's distribution theorem for signed
distances on a line, Euler's totient theorem
for congruences (mod 
)
of powers of the totient function 
, and Euler's triangle theorem (more commonly called the
Euler triangle formula giving the distance
between the circumcenter and incenter
of a triangle.
Euler's Theorem
See also
Euler's Displacement Theorem, Euler's Distribution Theorem, Euler's Totient Theorem, Euler Triangle FormulaExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Euler's Theorem." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/EulersTheorem.html