  Exceptional Belyi covering is a connected Belyi covering uniquely determined
by its ramification scheme or the respective dessin d'enfant. We focus on
rational exceptional Belyi coverings of compact Riemann surfaces of genus 0.
Well known examples are cyclic, dihedral, and Chebyshev coverings. Using Maple,
we identified all rational exceptional Belyi coverings up to degree 15. Their
Belyi functions were calculated for degrees up to 6 along with some for degree
7. We also found new infinite series.
