Center conditions and bifurcation of limit cycles at three-order nilpotent critical point in a seventh degree Lyapunov system

In this paper, center conditions and bifurcation of limit cycles at the nilpotent critical point in a class of seventh degree system are investigated. With the help of computer algebra system MATHEMATICA, the first 12 quasi Lyapunov constants are deduced. As a result, sufficient and necessary conditions in order to have a center are obtained. The fact that there exist 12 small amplitude limit cycles created from the three order nilpotent critical point is also proved. Henceforth we give a lower bound of cyclicity of three-order nilpotent critical point for seventh degree Lyapunov systems.