あ、簡単か
lim[n→∞] (1/n) Σ[1≤4k+1≤n] {n/(4k+1)}
= lim[n→∞] (1/n) Σ[1≤4k+3≤n] {n/(4k+3)}
= (1/4) ∫[0→1] {1/x} dx
でいいのかな？あん？