Alphabeta Math
TheoremStatement: Literature-sourcedProof: AI-adaptedprecheck passaudited 2026-08-24
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The real Gamma functional equation Γ(s+1)=sΓ(s)

Statement

For every s>0, Γ(s+1)=sΓ(s), and Γ(1)=1.

Facts & Assumptions

Given: A real parameter s>0 and truncation parameters 0<ε<1<R.

[F1]

If differentiable u,v on a compact interval have integrable derivatives, then ∫uv′=uv∣ab−∫u′v (If u,v are differentiable on [a,b] with u′,v′ integrable, then ∫abuv′=u(b)v(b)−u(a)v(a)−∫abu′v).

[F2]

The Euler integral converges if and only if its real parameter is positive (Euler's Gamma integral converges exactly for positive real parameters).

Proof

technique · direct
1.1givenF1

Apply [F1] on [ε,R] with u(t)=ts and v′(t)=e−t: ∫εRtse−t dt=[−tse−t]εR+s∫εRts−1e−t dt.

2.1step 1.1algebra

Since s>0, εse−ε→0 as ε↓0. At infinity choose a natural m>s; then Rse−R≤Rme−R→0 by exponential domination.

3.1step 1.1step 2.1F2

Letting the two truncations approach their improper ends in step 1.1 and using [F2] gives Γ(s+1)=sΓ(s).

4.1F2algebra∎

At s=1, Γ(1)=∫0∞e−t dt=[−e−t]0∞=1.

Depends on

Used by

Dependency tree · two levels

37 results within two dependency steps of this one, each drawn at its shortest distance from it. An arrow runs from a result to what uses it, so the chart reads left to right and ends at this result, which carries a heavier outline. Every node is a link to that result. Click elsewhere on the chart to enlarge it.

Sources