有一个数列aaa,规定a1=2,a2−a1=4,(an)−(an−1)=2n(n≥2)a_1=2,a_2-a_1=4,(a_n)-(a_n-1)=2n (n \ge 2)a1=2,a2−a1=4,(an)−(an−1)=2n(n≥2),若(1/a2)+(1/a3)+...+(1/an)=504/1009(1/a_2)+(1/a_3)+...+(1/a_n)=504/1009(1/a2)+(1/a3)+...+(1/an)=504/1009,求n
