>>940
Vk = 2π∫[0,π/k]kx*sin(kx)dx = 2π^2/k

Σ(k=n+1→2n)Vk
= 2π^2 * Σ(k=n+1→2n) 1/k
= 2π^2 * (1/n) Σ(k=1→n) 1/{1+(k/n)}
→ 2π^2 ∫[0,1] {1/(1+x)} dx = 2π^2 * log2