X(9), X(57), X(527), X(2291)
Foci of the Steiner in-ellipse, see also Table 48.
Foci of the Mandart ellipse (see Generalized Mandart Conics in the Downloads page and also K040)
K352 = nK(X6, X522, X9) is an isogonal focal cubic passing through the foci of the Steiner and Mandart inscribed ellipses.
It is the locus of foci of inscribed conics centered on the line G-X(9).
Its singular focus is X(2291).