Digital Library of Mathematical Functions
The Gamma Function -- Infinite Products

Infinite Products

Γ ( z ) = lim k k ! k z z ( z + 1 ) ( z + k )
z 0 , - 1 , - 2 , ,
1 Γ ( z ) = z γ z k = 1 ( 1 + z k ) - z k
| Γ ( x ) Γ ( x + y ) | 2 = k = 0 ( 1 + y 2 ( x + k ) 2 ) ,
x 0 , - 1 , .
k = 1 m a k = k = 1 m b k

then

k = 0 ( a 1 + k ) ( a 2 + k ) ( a m + k ) ( b 1 + k ) ( b 2 + k ) ( b m + k ) = Γ ( b 1 ) Γ ( b 2 ) Γ ( b m ) Γ ( a 1 ) Γ ( a 2 ) Γ ( a m )

provided that none of the b k is zero or a negative integer.