Catalan's constant

In mathematics, Catalan's constant G is the alternating sum of the reciprocals of the odd square numbers:

${\displaystyle G=\sum _{n=0}^{\infty }{\frac {(-1)^{n}}{(2n+1)^{2}}}={\frac {1}{1^{2}}}-{\frac {1}{3^{2}}}+{\frac {1}{5^{2}}}-{\frac {1}{7^{2}}}+{\frac {1}{9^{2}}}-\cdots .}$

Its numerical value is approximately (sequence A006752 in the OEIS)

G = 0.915965594177219015054603514932384110774...,

and it is also equal to β(2) where β is the Dirichlet beta function.

Catalan's constant was named after Eugène Charles Catalan, who found quickly-converging series for its calculation and published a memoir on it in 1865.