The Lester circle is the circle on which the circumcenter , nine-point center , and the first and second Fermat points and lie (Kimberling 1998, pp. 229-230). Besides these (Kimberling centers , , , and , respective), no other notable triangle centers lie on the circle.
The Lester circle has circle function
(1)
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where
(2)
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does not appear to have a simple form and does not appear in Kimberling's list of triangle centers. The center of the Lester circle is
(3)
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where is the circumradius of the reference triangle, which is Kimberling center . The radius of the Lester circle is given by
(4)
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where is a symmetric 16th-order polynomial that does not appear to have a simple form.
It is orthogonal to the orthocentroidal circle.