Digital Library of Mathematical Functions
The Gamma Function -- Inequalities

Inequalities

Contents

Real Variables

Throughout this subsection x > 0 .

1 < ( 2 π ) - 1 2 x ( 1 2 ) - x x Γ ( x ) < 1 ( 12 x )
1 Γ ( x ) + 1 Γ ( 1 x ) 2
1 ( Γ ( x ) ) 2 + 1 ( Γ ( 1 x ) ) 2 2
x 1 - s < Γ ( x + 1 ) Γ ( x + s ) < ( x + 1 ) 1 - s
0 < s < 1
exp ( ( 1 - s ) ψ ( x + s 1 2 ) ) Γ ( x + 1 ) Γ ( x + s ) exp ( ( 1 - s ) ψ ( x + 1 2 ( s + 1 ) ) )
0 < s < 1

Complex Variables

| Γ ( x + y ) | | Γ ( x ) |
| Γ ( x + y ) | ( sech ( π y ) ) 1 2 Γ ( x )
x 1 2

For b - a 1 , a 0 , and z = x + y with x > 0 ,

Γ ( z + a ) Γ ( z + b ) 1 | z | b - a

For x 0 ,

| Γ ( z ) | ( 2 π ) 1 2 | z | x - ( 1 2 ) - π | y | 2 exp ( 1 6 | z | - 1 )