ここまでのまとめ

π
=lim(n→∞)nsin(π/n)
=lim(n→∞)Σ↑∞↓n=1 ((-1)^n/2n+1)
=lim(n→∞)√(6 Σ↑∞↓n=1 (1/n^2)) 
=lim(n→∞)√(6 Π↓p (1/(1-1/p^2)))