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X(110), X(691) centers of Apollonian circles 

Given the isoconjugation with pole W = X110^2 (barycentric square of X(110), the locus of point P such that the pedal triangles of P and its Wisoconjugate P* are parallelogic is K147 = nK0(W, X6) = cK0(#X110, X6), if we omit the line at infinity and the trilinear polar of the isotomic conjugate of the isogonal conjugate of W. K147 is a member of the class CL022 of cubics. It is a singular cubic with node X(110) and with perpendicular nodal tangents. See Special Isocubics ยง8. The isogonal transform of K147 is K979. See here for a family of related cubics. 
