Basel Problem as Infinite Product
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Theorem
- $\ds \dfrac {\pi^2} 6 = \prod_{p \mathop \in \mathbb P} \dfrac {p^2} {p^2 - 1}$
Proof
From Sum of Reciprocals of Powers as Euler Product:
- $\ds \sum_{n \mathop \ge 1} \dfrac 1 {n^z} = \prod_p \frac 1 {1 - p^{-z} }$
for $z \in \C$ such that $\map \Re z > 1$.
Putting $z = 2$:
\(\ds \sum_{n \mathop \ge 1} \dfrac 1 {n^2}\) | \(=\) | \(\ds \prod_p \frac 1 {1 - p^{-2} }\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds \prod_p \frac {p^2} {p^2 - 1}\) | multiplying top and bottom by $p^2$ |
The result follows from Riemann Zeta Function of $2$.
$\blacksquare$
Sources
- 1986: David Wells: Curious and Interesting Numbers ... (previous) ... (next): $3 \cdotp 14159 \, 26535 \, 89793 \, 23846 \, 26433 \, 83279 \, 50288 \, 41972 \ldots$
- 1997: David Wells: Curious and Interesting Numbers (2nd ed.) ... (previous) ... (next): $3 \cdotp 14159 \, 26535 \, 89793 \, 23846 \, 26433 \, 83279 \, 50288 \, 41971 \ldots$