>>593
cos(π) = - 1,
cos(2π/3) = - 1/2,
cos(2π/5) = (√5 -1)/4 = 1/(2φ) = 0.309017
cos(2π/7) = 0.6234898
Π[p≧11] cos(2π/p) > Σ[p≧11] (1 - 2ππ/p^2)
　　> 1 - Σ[p≧11] 2ππ/p^2
　　> 1 - (2ππ)Σ[k≧5] 1/(2k+1)^2
　　= 1 - (2ππ)(ππ/8 - 1 - 1/9 - 1/25 - 1/49 - 1/81)
　　= 1 - (2ππ)・0.0498356
　　= 0.01628475
∴　(与式) > 0

なお
　Π[p≧7] cos(2π/p) = 0.3338
　Π[p≧11] cos(2π/p) = 0.5354
(与式) ≒ 0.05158