Marinada '18

Neka je \(a_1 = \frac{4}{3}\) te: \[a_{n+1} = a_n - \frac{4}{(2n-1)(2n+1)(2n+3)}\] Odredi: \[\sum_{m=1}^{\infty} (a_m-1) \prod_{n=1}^{\infty} a_n\]