|z| = 2√3,
z = (2√3)e^{ｉ(7π/6)},
|z|^8 = 12^4 = 20736 < 30000,
|z|^9 = 41472√3 > 30000,
∴ n≧9
z^9 =｜z|^9 e^{ｉ(3π/6)},
z^10 =｜z|^10 e^{i(-2π/6)},
z^11 =｜z|^11 e^{i(5π/6)},
z^12 =｜z|^12
z^13 =｜z|^12・z
∴ n=13